I think of just selling a new wallet.dat which helds the amount of sold BTC and transfer it encryptet.. after receiving money, they get the key. What do you think?
This is kinda OT here, so you may want to start a new thread. Anyhow, as a potential buyer, I'd be pretty uncomfortable with this as you may not send me the (correct) key, or keep a local copy of the wallet and empty it as soon as the money arrives. It'd put me in a pretty vulnerable position.