I once worked at a startup that took payments on behalf of charities. Due to the pick-your-price nature of donations there'd be a lot of users who've bought or

I once worked at a startup that took payments on behalf of charities. Due to the pick-your-price nature of donations there'd be a lot of users who've bought or stolen credit card information testing to see which ones are still active by making charges small enough to go unnoticed. What sucked is that the charity would then be charged a fee when the card holder reversed the transaction.