Datapoint: I've purchased probably $12,000 in GCs from Cardpool this year. I've had a few duds - where I got the card and it was empty, or they sent me an invalid eCode - and in each case they've quickly refunded my money. Their customer service has been exceptional for me over the last year.

No experience in selling gift cards to them though.

Figured I'd pass it along. They don't always have the best discount %, but I'll go w/ Cardpool over some of their competitors, just because I'm confident they'll refund me if I get a dud.