If I deal with BTC I personally accept the transaction to be valid after the first confirmation.
It will be a very hard coincidence, that the sender is prepared to do the double spent and the block with my transaction got marked as invalid.
Of course, it is possible, but I have never seen this with my own eyes.
Especially in a face to face meeting, you can see, if the other person is trying to do a double spent.
Of course, it depends on the amount you are sending and the trustability of the counterpart/sender.