Bitcoin Forum

I have done loads of transactions and all my unconfirmed transactions have been confirmed and bitcoin credited

Some merchants will ask customers to wait for the confirmations but what is the actual risk? and what could happen other than the transaction being confimed?

I made one without fees that did not get confirmed for ~8 days IIRC. I had to double spend it, which is what merchants are afraid of. After enough time has passed most (if not all) nodes will forget about the transaction and its unlikely that it gets confirmed. I could create another transaction that spends the same inputs, but instead of paying the merchant I pay someone else. Should my new transaction be confirmed the old transaction becomes invalid and can never be confirmed.

I see, this would mean that there is a lot of transactions that will never be confirmed..

But if money left my btc address and will never reach recipient's btc address where does the money go then?

The money does not leave your btc address with an unconfirmed transaction: the network considers it still there and did not move.
The unconfirmed transaction will eventually be dumped from the nodes mem pool.
If your wallet thinks it has been spent, simply make sure to synchronize it or import the private key in another (better connected) wallet.

People can double spend and have the btc fail and come back to them. So the merchant loses btc.

Which payment processor did that merchant use for your order?

Aren't they are able to seperate transactions with and without any fees?

That's quite an important feature, especially for the protection of merchants.

I had one without fee and it took almost 10 days to get first confirmation,if your transaction is legll, then it will eventually get confirmed.

I did not order anything, I made a TX to myself in order to fuse 4 small inputs into a bigger one without paying a fee. It failed, I paid a fee. It could have been a payment to a company though.


Sure, a merchant can also rebroadcast my transaction without fee which would make it very difficult to double spend it. There are several counter measures to double spends. E.g. a company could contact a miner directly and to get such a transaction confirmed with priority even though it has no fee.


I have yet to see a service that refuses payment if the transaction has no fee. A high priority TX without fee will confirm fast anyway, its not like the fee is the only indicator.



While thats not wrong eventually might be a very long time. I still have an input for 1 satoshi. I would have to wait ~10 million days for it to have a high enough priority to get confirmed without fee.

Just to be on safeside and avoid double spend

i think the biggest risk and what is most probable is the double spend. as long as the transaction is not yet confirmed the coins are not spent so they can be sent to another address

It can sometime not get accepted by miners because of lower or no fees or maybe you try to spend it before confirmation somehow

Yes had one or two. I think I issued it with MultiBit, although I'm not completely sure it was the fault of MultiBit, the relaying servers or it getting lost between the nodes or left in the mempool somewhere...

I had a reception transaction that was not coming through because it was sending a small transaction back to the original wallet

thanks for the answers.

how are miners aware if a transaction is sent with or without fee? and how can they select a specific transaction?

I though bitcoin didn't discriminate people in that transactions are processed in order from when they were submitted..

someone mentionned "A high priority TX" what is that?

They have them stored on their systems memory and can analyse them, same as every other full node. Thats how blockchain explorers do it and you could do it with your local copy of e.g. bitcoin core/qt as well.


Transactions have no "timestamp" thus its impossible to mine them in chronological order of creation.


The priority of a transaction depends on the size of the input you want to spend and the age (how its been confirmed). A detailed formula can be found here[1]. A rule of thumb is that 1 Bitcoin confirmed for 1 day (1 bitcoinday) will have a priority high enough in order to get confirmed without fee in reasonable time. 0.1 Bitcoin would take 10 days, 0.01 100 days, while 10 Bitcoin would take ~144 minutes.

[1] https://en.bitcoin.it/wiki/Transaction_fees#Technical_info

for example when i withdraw from localbitcoins the site takes a transaction fee but on the blockchain this fee is not shown, only the amount that i requested to withdraw is shown so how are miners aware that i payed a transaction fee?

thanks

Are you sure? I have never, ever heard of a merchant that will actually make a customer wait.

Does that same merchant also ask customers to wait 6 months when paying with credit card, until the chargeback period expires?

Theoretically, the transaction could end up never being mined, thus effectively the merchant wouldn't receive the bitcoins. But theory ≠ practice. For real, live, actual every day paments, this is a totally insignificant risk. It just doesn't happen.

ive had a few where i didnt send a fee. some transactions took a few hours

Some bitcoin businesses accept instant deposit and payments without waiting confirmations but it is rare because they are probably losing money doing that.

Oh! never knew some do , AFAIK they atleast go for 1or 2 confirmations

If you buy some goods that worth $200, would you want to spend lots of work to produce a fake block?

If you the goods worth $200,00, merchants will wait for enough confirmations

yep! no one will take risk over that big amount

No, pretty much any regular business that accepts Bitcoin, does so without ever waiting for any confirmations. Think about it - it'd be ridiculous to make a customer wait 10 minutes (or more) at the cash register before they can leave. They don't do that with credit cards either, and the chargeback risk is actually real there (unlike Bitcoin).

The exception is exchanges, they will typically await a few confirmations before updating your balance, but that's more like a deposit or cash transfer, not a case of live or real time paying for goods or services.

I have had unconfirmed transactions not going through, but that was in my early BTC days, when I was experiencing with dust from faucets.

It's only natural for a merchant to wait for a transaction to be confirmed. The same thing used to happen in shops when a customer was requesting to pay by check. The shop would have called the bank to confirm the check was good. The problem was solved with shops not accepting checks anymore.

Yes  i hate the waiting time

That could happen , seeing the chances of double spend are quite low and here are no chargebacks

Why would it be rare? There are plenty of merchants with bitpay implementation accepting 0 confirmation transaction. A double spend is not as easy as you think. As long as you wait 30 seconds or so, connect to well connected nodes and the transaction is well propagated, a double spend is unlikely but not impossible.