However, various payment processors have requirements that the transaction must have at least 3 or even 6 confirmations in order to be valid, so for a less knowledgeable user, paying with BTC can sometimes be quite confusing, especially if he has the misfortune that the time between blocks is unusually long.
I can still understand that for large amounts it makes sense, but for some smaller transactions worth a few tens or hundreds of $, nothing more than a maximum of 2 confirmations makes sense.
The misconfiguration that hosemary mentioned happening more than a decade ago lasted for a few hours. The problematic transaction was valid for multiple blocks before the block was finally orphaned. It's safe to assume that it had the needed 3, 6, or x confirmations. An orphaned block in itself isn't that big of a deal. The transactions that made it into that block go back to the mempool, waiting to be confirmed again. People don't necessarily lose the bitcoin they previously had. They just have to wait for confirmations again. Unless, of course, someone doublespends the coins.
