Someone once came up to me straight after a song while on stage at a festival and loudly asked how much my CDs were, followed up by, can I swap for one of mine. The most tactful thing I could think of was to say yes, figuring that the actual cost of the CD wasn't worth worrying over it.

I bumped into him the following year, he told me how much he'd enjoyed the album. Which is way, way more than I could say in return....