CSSmania: Our way of fighting SPAM with submissions
blog.cssmania.com
blog.cssmania.com
They're a payment processing company, not a free security deposit holding service. Visa and MasterCard also enforce maximum return rates (as a percentage of processing volume), so PayPal has incentive not to allow this kind of use of their service.
However, a lot of people genuinely think what they list is good (just watch an episode of a talent show audition and see how surprised people get when you tell them they are shit).
So you'll still get loads of people submitting, but you'll have the added time-sink of dealing with those people who thought they were good enough, lost the $10 and now opened a case against you on PayPal.
My advice would be (if you're going down the charge route) to simply charge everyone for submission and don't give the money back whether they make it or not.