Tell me about a time where you gave or sacrificed something and received something else back 10-fold as a result.

A bank once mistakenly paid me out a second time on a single, substantial money order from overseas. They didn't correct it and I was tempted to say nothing but after a few weeks I informed them of the error, afraid that it would catch up with me later.

My honesty had its reward: They responded that they didn't make that kind of mistake and unless I had evidence to the contrary I should close my files on the matter. I did just that. I sometimes wish I could figure out how it happened, for potential future use :).