[pyalot2]

There different ways to implement escrow with bitcoin.

1) You could ignore all technicalities and simply send the coins to a third party which releases it back to you or forward to the merchant. That's probably the least recommendable way, but is the easiest to explain.

2) A smarter way to do it is to use bitcoins transaction script that can process multi signature transactions, which can work in a way that if A wants to send B money, he can setup an address that can only withdraw coins from if C also signs the transaction. This method is supported by Electrum and by the Blockchain.info wallet.