There are do-it yourself (DIY) approaches (see the Bitcoin.it wiki for Shopping Cart Interfaces) and then there are payment processors who can help (e.g., BitPay, WalletBit, Coinbase, Mt. Gox merchant tools, etc.)

Even with a payment processor though you need to be knowledgeable about double spends:
 - http://en.bitcoin.it/wiki/Double-spending

If you ship goods out, then you can protect from double spends by holding orders until the payment has fully confirmed (reached six confirmations, or at least three).   

If instead you need to process and deliver the purchase immediately (e.g., sale of a prepaid gift card e-code that can be used for purchases at a retailer immediately) then you do expose yourself to a much greater risk of a double spend from a "race attack".  Few businesses have a profile where this is a risk (SatoshiDICE is one example, and maybe an automated coin dispenser at an unattended laundromat might be another example) so it boils down to where if the there is no economic incentive for the attacker to attempt to double spend then that alone will keep the number of occurrences in check.

This works best when being developed by the exchange itself.   There are none that have released this yet.

Fairly comprehensive directory of exchanges:
  - http://en.bitcoin.it/wiki/Buying_bitcoins

Well, what happened was that someone somewhere cheated you by sending you funds that might have confirmed but then were later double spent.  During the period of time while the transaction you received had one confirmation you then unknowingly ended up propagating this cheat to some else (SatoshiDICE) by sending a payment with funds that will never confirm and included a double spent coin.

This transaction back in your history that had cheated you probably came to you from SatoshiDICE.   And if true, then prior to that the funds to them were sent by someone trying to cheat SatoshiDICE.   So SatoshiDICE had no intention to cheat, but they didn't take proper precautions from sending the "potentially bogus" payout to you.

When they do that (and it is too bad they won't take the actions that would cause their service to stop doing this to people), what they end up doing is having to fix the problem at a later time by sending out a replacement payout.  The later replacement payout confirms just fine.

Now you are affected by this negatively because the Bitcoin-Qt client does not handle this condition where a transaction has at least one confirmation and is used in a payment but then at a later time that confirmation vanishes as the result of being double spent against.

This situation where a transaction has at least one confirmation and at a later time ends up being a double spend is something that occurs rarely.  For this reason, supporting this condition in the Bitcoin-Qt/bitcoind client has not been a feature that has made it into a release just yet.


No, they didn't vanish they simply are stuck in transactions that the client doesn't know how to handle as far as canceling after a certain period of time.

So remedies at this point are:
 1.) Use joric's fork of pywallet and remove all transactions.  Then -rescan.  

 2.) Create a hybrid EWallet from your wallet.dat.   Use  https://blockchain.info/wallet/import-wallet

3.) Export your keys, then create a new wallet and import the keys into the new wallet.

From Mt. Gox's Withdrawal Center you can do an International wire transfer of your USDs (or GBPs).  Mt. Gox charges a fee as will likely your bank, so this method is not inexpensive -- especially when the amount being withdrawn is small.

Some people make use of the ability to withdraw to OKPay.  OKPay funds can be spent using an OKPay debit card.

From there the list of options shrink.

You might be able to find someone willing to trade with you where you provide a Mt. Gox redeemable code (either GBP or USD, whichever you have) and in exchange you get the funds through a bank transfer.  You'ld only want to do this with a trusted counterparty.  The #bitcoin-otc marketplace's Web of Trust (WoT) will help as it has a trust history.
 - http://www.Bitcoin-OTC.com
 - http://webchat.freenode.net/?channels=#bitcoin-otc-foyer
 - http://webchat.freenode.net/?channels=#bitcoin-otc-uk  <-- Specific to UK

Instead of selling coins at Mt. Gox you might want to consider a different exchange.  BitBargain is one method:
 - https://bitbargain.co.uk/

And, of course, you have many local cash out methods:
 - https://localbitcoins.com/postal_code/uk/london/

And individuals who will buy your coins:
 - http://bitcointalk.org/index.php?action=profile;u=65105
and
 - http://bitcointalk.org/index.php?topic=130949.0

One method to short sell is to personally borrow bitcoins, sell them on the market, and then buy them back later when the loan repayment(s) is(are) due.   Of course, that's a naked short and nobody will lend you any significant amount of bitcoins without collateral or other assurances the lender may require.

Other methods include selling the BTC/USD futures contracts at ICBIT.se.

Currently they have a March 15, 2013 contract expiration, April 15th, 2013, June 15, 2013, and a September 15th, 2013.   You can get somewhere around 10X leverage this way, but be careful at those higher levels as volatility can easily put you in a position where your margin is insufficient and you et a margin call (and see your positions liquidated by force).
 - http://www.ICBIt.se

Additionally you can buy PUT contracts (or write CALL contracts) on MPOE/MPEX.

Coming soon are CoinSetter, Kraken and more.

LocalBitcoins might be your quickest path to getting some coins, depending on where you are.

Also, there are several other methods:
 - http://BitMe.com (deposit cash at Chase)
 - http://BitFloor.com (deposit cash at Bank of America)
 - http://Ziggap.com (deposit cash at Bank of America, and soon returning, Western Union)
 - http://BitInstant.com (deposit cash at 7-11, Walmart, CVS, moneygram locations)

Use only clients that are open source.  Use the most widely used and supported open source client to ensure that many, many eyes are looking specifically at that part of the code.   Use only official releases or build from the source yourself so as to ensure nothing slips in. 


There are varying levels of security needed for various use profiles.  The bitcoin address created by the Javascript source running in my browser might be entirely sufficient for the way I intend to use it.  Anyone safeguarding a million-dollar wallet might have differing requirements and use whatever method is appropriate for the specifics for that profile.  (Though the Javascript method running from an offline browser booted on a LiveOS image is probably going to provide the same level of security.)

I had bought one to use for show, like here's a 1 BTC and then here's a 25 BTC coin -- the "coin collector" version.

It really is an attractive coin, the reverse even more so brilliant than the obverse.   But I didn't feel comfortable carrying that around as the value started to rise.  I remember getting worried when it was being passed around at an event so I decided to just redeem it so that it could still be passed around and I wouldn't have to worry much if it disappeared.

So these would be intended for single use?  e.g., If I gave it as a tip, the server would either keep it for saving, or redeem it or would send it to a cash-out/exchange service?  (i.e., rather than spend it by handing it over to someone else?)

Well, BitFloor doesn't set the price.  The price you pay depends on what other traders are willing to sell their coins at.  

If you were patient and put in a bid at a price, let's say $2 over Mt. Gox market price, you probably would have gotten your order filled within an hour or two.   Normally the difference between BitFloor and Mt. Gox is much smaller, and sometimes you can even buy below the Mt. Gox price.

So what you saw was the herd of people unable to use BitInstant all swarming the sellers on BitFloor.  So of course you ended up overpaying.

To get more sellers noticing the arbitrage opportunity, I used to see people announce their intentions (e.g., buy volume and what they were willing to pay) on a forum thread and/or in the #bitcoin-otc IRC channel.  That way sellers could have time to get coins deposited and put sell orders in to be able to score a nice trade.

So to summarize, your next transaction paying cash to buy coins at BitFloor will probably result in a better experience.  There is also BitMe.com which you could try.  They use cash deposits through Chase and have a different order book -- currently even lower than BitFloor's.

Doh! I knew that was a risk.  So had I sold those BUH3's yesterday at $40+ I would have kept my profit but because I pushed my luck I see part of my position sold at a lower thirty-something level because some anonymous trader was too short.

Doesn't this make the perfect scam opportunity then?  

Scammer opens two accounts, long and short.  
Long account is used to buy at about 5X leverage.  Each buy is matched with a sell from the short account, also at 5X leverage.
Wait for rip roaring rally or selloff.   Upon receiving first margin call notice on either the long account or the short account, close out positions on the other account that has the gains, maybe even use the account with the negative balance to provide liquidity (assuming a short can still buy to close, for example, when the account is negative).  Then the profitable account withdraws the coins (variation margin is already settled when the position is closed).  Two days later (or whatever the delay is) other customers with profitable positions see forced trades to cover for the negative account.

This is where leverage/margin accounts + anonymity don't mix.

It means someone somewhere cheated you by sending you funds that never confirmed and instead were double spent.  You then unknowingly are propagating this cheat to someone else by sending a payment with funds that will never confirm and include a double spent coin.

This transaction back in your history that cheated probably came to you from SatoshiDICE.   And if true, then prior to that it was sent from someone trying to cheat SatoshiDICE.   So SatoshiDICE had no intention to cheat, but they didn't take proper precautions from sending the "potentially bogus" payout to you.

When they do that (and I wish they would stop doing it), what they end up doing is having to fix the problem at a later time by sending out a replacement payout.  The later replacement payout confirms just fine.

If you were using the Bitcoin-Qt client this probably wouldn't have happened to you.  Bitcoin-Qt won't let you spend a payment that you've received without first ensuring it has at least one confirmation.  (Technically this could still happen with one confirmation, and thus from the Bitcoin-Qt client as well though that occurring is generally pretty rare.)

But you are using Blockchain.info/wallet which will gladly spend funds that haven't yet confirmed.

To avoid this in the future, use Bitcon-Qt ... or maybe stop gambling [Edit: with a service that will send you bogus payouts].  :-)

Over the long run that affects new supply and thus weighs in on price discovery where supply and demand meet.

Over the short run, the exchange rate is determined by organic demand (you can't send a bitcoin across the blockchain unless you've acquired it first), speculative interest -- how much traction is bitcoin getting / will it be seeing wide use as a competitor to PayPal and/or Western Union, will bitcoin see traction as a payment method at retail, will Bitcoin compete against SWIFT payment messaging network, etc.   

Add all that up and you get the current market price.

Unfortunately the Bitcoin-Qt/bitcoind client does not know how to purge these double spends.    As you realized, if the transaction includes not just the double spend but other inputs the client doesn't show those as being avail

There are several ways of resolving this.  

One is to export your private keys and then import them into a new, empty wallet. Bicoin-Qt has a debug menu where these commands can be entered.
 - http://bitcoin.stackexchange.com/a/4633/153

The other is to use the pywallet utility to delete all the transactions and then restart with -rescan to have the balance recomputed properly.  If your wallet has passphrase encryption then you'll need joric's fork, not jackjack's.

Another approach is to create a new wallet at Blockchain.info:
 - https://blockchain.info/wallet/import-wallet
and then create a new empty wallet on your Bitcoin-Qt client (and spend the funds back to your new wallet).

[Edit: If you are still stuck or need assistance, you probably could find someone trustworthy willing to help -- for a fee.  This would only be if you never expect to receive more funds at any address in your wallet.  What you do then is send your wallet.dat plus a new Bitcoin address (where you would like to have your recovered funds sent) and the person you hired performs the work of recovering the funds.]

And the hits keep on coming!

- http://blog.bitinstant.com/blog/2013/3/4/events-of-friday-bitinstant-back-online.html



Losses of $8K USD are immaterial?  I suppose "Major" means something different nowadays.   Does BitInstant's $12K loss even qualify then?

I'm confused.  If it was a profitable position it would add variation margin and thus no payment would be required.   About the only thing that would explain a profitable position seeing forced margin selling would be if the margin requirements changed, which if true would be news to me.

You might be able to see if the author of that is interested in helping with that. 

It is open source (MIT license) so you can hire someone to fork it and add the feature you want.  If it is made as a configurable option, then that would make it so that the change could be merged in to the main branch upstream.

I think tgmarks is the author of that project, though I'm not entirely sure:
 - http://bitcointalk.org/index.php?action=profile;u=48283

Looks like someone with a short got liquidated on a BUH3 short position?

Showing bids getting filled all the way down to $34.2.   Dammmnn, so I guess it would have paid for me to have left a few lowball bids out there just in case this type of event happens, it appears.

Probably is explained here:





Your wallet at DeepBit is a hosted (shared) EWallet.  What this means is that you don't have control over the coins but instead are just sending a withdrawal request to DeepBit and then they service that request.

Thus if you want the control over your own funds, DeepBit or any other hosted (shared) EWallet provider is not the place to store your coins.   A local Bitcoin client such as Bitcoin-Qt, Multibit, Bitcoin Wallet for Android, or even a hybrid EWallet such as Blockchain for Android and iOS will be better options for you if you need a guarantee that you can send payments without any delay.