Store accidently sends me an extra ipod, and now wants it back.

[GT123]

So I order a a 80g ipod video with my fpps, and 1 week after I recieved my ipod, a second one came in the mail. I gave the Ipod away to my sister, who is visiting and is leaving tomorrow. Today an employee from the electronics store calls, telling me he sent me an extra ipod by accident, is in trouble and wants me to send it back via courier.

Should I send it back? What can they really do if I decide not to send it back?

Has this ever happened to anyone? Seems odd to me that a big name electronics store wouldn't just write this off, instead of having the employee that made the mistake call me and try to get it sent back.