That's why while dealing a transaction personally, you should wait for 3 confirmation before making transaction from your side to be sure of. Ask for a good fee transaction to start with but if they insist, let them know you'll need to wait for confirmation. It doesn't just happen daily but you need to be safe than sorry.
Waiting for three confirmations is even an over kill. One confirmation is ok to guarantee the transaction won't reverse. Buyers should always insist on that, especially if they're dealing with unknown persons. I even encountered a suspicious case similar to that a few hours ago. What these scammers do now is to make you a mouth watery offer, either selling ridiculously cheap or offering to buy at any price you make them. Be careful or you kiss your hard earned cash goodbye.
