Quote from: g4qoj7 on March 27, 2012, 12:42:32 PM

I'm planning to buy some bitcoins at my campus and pay in cash.
However, I don't want to give the money until I'm sure the bitcoins have been transferred to my wallet.

Is it an instantaneous operation? I mean, Will I see the bitcoins in my running client some seconds after the seller send me them? How long does it take?

Gracias por adelantado.

Your client should be able to see the transaction within a few seconds, assuming that it is a valid transaction, but it won't let you spend it until it's been included into a block and 'confirmed' several times. As the other responder said, he would have to be a master cracker to take it back before one confirmation and God after six confirmations.