I sold an amp to someone on here once, they got it, and said it didn't work fine, so I said send it back and I will refund you.
I got it back, it worked perfectly fine, so I sent him the money back minus the postage cost, however if it was broke when I got it, I would have refunded that too of course.
I always prefer pick up just to avoid this now though, I want someone to be there at mine, to test it's working before they walk away with it, then if it stops working, it's clearly a new fault.