He's only offering to represent you at the treasury auction with your bid. It's a scam.
Your bid is what he bids at the treasury auction. If you bid too high you win the car and he keeps the difference. If you bid too low, you lose at the treasury auction, but you still owe this clown your winning ebay bid. Your other option is to increase your low bid up to a point where you win the treasury auction, but he will charge you 2% of the increase. Nothing to stop him from having a shill bid against you at the treasury until his 2% is a sufficiently large amount. When you're at $40k you're more likely to keep increasing your bid rather than walk away with a big loss and no car.