In one of my former jobs, I was involved in selling defaulted/underperforming business loans. We generally pooled small loans, and offered larger loans individually. We had a list of generally interested parties whom may have been interested in purchasing our loans, and we accepted offers for a certain period of time and took the best one above our lowest acceptable price. Basically a silent auction with a reserve price.
It seems that prosper must pool these small loans and sell them in some sort of auction format, and since some loans don't sell there must be some type of reserve price for each pool. Therefore to get them in any sort of legal trouble you would have to bid on a pool of loans via prospers chosen auction/distribution channel and then have your offer be refused despite it being the highest offer, you can't just send them a letter.
If you think prosper is not getting as much as they could for these loans, your first step should be to find out how they sell them, and get involved in that process from the position of a potential buyer. Though, given that these are pools of significantly past due usecured consumer debt from mostly sub-prime (to say the least) borrowers, $0.08 on the dollar seems pretty fair to me.
acecapital