Stephen nailed it. The larger thing to take away is that everything in life is reversible. Everything. Bitcoin is reversible under certain conditions (0-confirm double spend, finney attack, sybil attack, 51% attack, etc). Bank wires can be reversed (no you can't hold a gun to Warrent Buffets head and make him wire $40 billion to your bank account and then say "sorry bank wires are irreversible"). Even cash can be "reversed" (counterfeit bills or someone hits you with big wrench and "reverses" the money back into their pocket).
So thinking about things as reversible or not reversible as if it is black or white, true or false, is a good way to get scammed.
Think about things in terms of
HOW DIFFICULT IS THIS TRANSACTION TO REVERSE (because remember EVERYTHING IS REVERSIBLE)On a scale of 1-10 (just my opinion)
10 - Multiple confirmation Bitcoin transaction
9 - Bank wire, 1-confirm transaction, cash deposit
8 - cash paid MoneyPak w/ receipt, 0-confirm Bitcoin transaction, cashier's check (after 7 days)
...
5 - ACH (and ACH based transactions like Dwolla, Popmoney)
....
1 - PayPal, other credit cards
So if you think of the "RISK OF REVERSAL" as a scale you can compare it to the scenario (do you know the person? do you trust the person? how much does the person have to lose? how large is the transaction? have you completed other transactions in the past? are they still inside the reversable window?)
As an example, when we sold wireless refills for Bitcoin we accepted <gasp> 0-confirm transactions from repeat buyers. Oh noes 0 confirm can be double spent. It was a calculated risk. Repeat buyer, someone I know, a small value transaction and the risk is still lower than a CC. On the other hand I am not going to accept a 0-confirm tx as sufficient security before handing over $20,000 in gold Bullion in person to person transaction with someone I don't know (who has his getaway car engine running).
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