I want my BuddyPress members to be able to accept donations. I want their pool of money to be kept on my side and then I pay out automatically when they want it withdrawn but I keep a percentage of the money. Users you donate can ask for refunds from individual members and members can give the refund but that's up to those involved in the transaction. Not the website. If they withdraw and they have no money on their account they will have to deposit money there first.