A donation system that gives you points to purchase items is a cash shop, not a donation. You can write a terms of service, donation rules page or whatever, it doesn't change much and I doubt PayPal would even read it. If somebody used a stolen credit card, or can prove a unauthorized access chargeback or said they never received anything, which you cant prove they did, then theirs a decent chance they'll get their money back. There's a lot of luck, I've won chargebacks I shouldn't have won and I've lost chargebacks where I actually lost something like game accounts, virtual goods, donation items and more. All I'm saying is, If somebody donates 100 euro, they probably will charge back and know how to do it properly and win, or it wasn't there money to begin with. If you go negative in PayPal long enough, they'll shut down your account and start calling your house number lol.