GMAB. The borrower is then reimbursing you for your bid. Either way, the $50 ultimately comes from the borrower. You risk zero of your own money. You are selling an endorsement and you are not even lending the borrower any money!
Edit: I'm trying to stay on topic here.
Just because you risk zero of your own money doesn't mean that the bid is not your own. I don't see anything in the TOS saying that you have to risk your own money.
Here's a question that I don't know the answer to (don't care to take the time to find the answer). If a friend gives me money to bid on a loan for him, is that against the TOS? My gut says no, yet I wouldn't be risking my own money.
I don't know whether it would be allowed. That's beside the point. The point is this:
1. You're violating Prosper's TOS.
2. Your endorsement would be completely worthless. That's fraudulent in my book, even if it's not against TOS to make worthless endorsements. It's fraudulent because you would actually have incentive to endorse lousy borrowers as well as good one, since you risk nothing at all. You may not call it fraudulent--we can disagree about that--but it certainly makes you look like a sleaze.
Oh yeah, the other point is :
3. You're shucking and jiving to make it look like you didn't really mean it. More sleaze.