I would say 1 confirmation is more than enough but if you really want to make sure just check out your own wallet and see the money there. If you see the money on your own wallet then there is no need to wait, some wallets accept 1 confirmation but there are plenty of them that wait until 6 confirmations which may take a lot of time but if the seller spends a decent amount of transaction fee then it shouldn't take more than couple hours at most and in which case you can have like a lunch or dinner or whatever together and talk about bitcoin. So, the short version is yes 1 confirmation is enough the long version is wait until you have the coins in your wallet to spend (which could be as much as 6 confirmations). It all depends on how much you trust your wallet and the seller.