72 hrs is the legal period within which funds can be reversed. This applies to Paypal, wire xfers, CC's and even money orders (yes money orders can be reversed & also can bounce).
You were the victim of a person who knew how to use the banking system in general.
If you have commercial banking accounts, cc processing etc... you get familiar with these things. The average person on the street is unaware of how these things can operate and be manipulated.
The bottom line is extend your caution to all banking processes, not just paypal (very poor system I agree), ebay etc...
In the future wait 72 hrs to xfer product no matter what method is used for payment. With CC purchases etc... I always wait 3 days unless the buyer has a track record with me ( I do not trust other "track record" systems).
