Is a Kevlar vest a "sham" because the wearer can still be killed by a shot to the head?
No, because a Kevlar vest isn't intended to stop a shot to the head. A Kevlar vest that doesn't stop a shot to the chest, within the ratings of that vest, would be defective. A Kevlar vest that is advertised as being able to stop a .357, when the advertiser knows full well it won't stop a .22, would be fraudulent.
A bidding endorser is intended to give lenders a certain level of confidence in the listing. When borrowers make side deals to pay back endorsers outside of the loan repayment, that endorsement becomes meaningless, if not fraudulent. Maybe calling the entire concept a sham was a bit harsh. It might be more accurate to call the implementation of that concept faulty.
Any bidding endorsement that isn't sufficiently large enough to hinder side payback deals should be considered suspect. For suspect endorsements, it becomes a matter of "how much do you trust the borrower?", which is the major question with any listing.
My point is, if a few low-dollar bidding endorsers make the difference in whether or not one trusts the borrower, then one should probably think again about bidding on the listing. If, however, one has got a listing he is pretty comfortable with and a couple of snickers and a milky way helps to ease his mind further, that's nice, but, it's about as meaningful as a snittybee guarantee. Dismissing an otherwise solid listing simply because it doesn't have a bidding endorser gives bidding endorsers a lot more weight than they deserve.