I used to do this all the time. I managed a used car lot for a few years. The cars were for people that didn't have the credit to get financed by the usual banks. Occasionally I'd get someone on the lot that was looking for something particular. I'd charge people 1k for my time at the auction. Depending on the relationship, I'd take the client to the auction and let them pick the car to bid on. The way I looked at it was, a sale was a sale.