People can pay you thousands $ over PayPal, but you get nothing at the end

I am the author of www.Photopea.com . Some people pay 9 USD a month for a Premium account.

Then, some users report it as "unauthorized payment". As I don't want to spend time on arguing, or get bad reputation, I agree to return the payment.

Then, PayPal returns these 9 USD back to the user, but also, makes you pay a 20 USD fee for who knows what :/

If users make 1,000 payments: 9,000 USD, and one of three users reports "unauthorized payment", you would say you end up with 6,000 USD (as you return a third of money). But acutally, you end up at -660 USD (as PayPal takes 333 * 20 USD as fees).

I just think it is an interesting fact, that PayPal can take all your money in extreme cases. I would like you to be aware of these fees, if you are planning to accept money via PayPal.