I think the idea of incoporating real money into this is very risky. Even if you do have several steps for a custom to be approved, there will always be ways around it. (I can't really think of any rn, but just keep in mind that almost every idea has its negatives.) Plus, think about the bugs. What if, perhaps, you purchase a custom but you never get it? It's best to stay traditional and go on other GFX websites or ask artists to make customs for you.