I'm sure the seller is thinking of preventing timewasters by asking for the deposit.He's probably doing it to stop timewasters. As in go and collect the car within 48 hours of the auction ending. He does encourage viewing before you bid, which is always adviseable.
But in reality they are expecting everyone to accept that they are genuine, and the car is "as described"
And asking for £500 and saying it's non refundable?
That's just silly.
I've always found Ebay auctions never get's the best buyers.
You're asking someone to bid with out seeing the car, well you're never going to get the best price as you'll be putting so many genuine buyers off who darn't bid on something they haven't seen.
Best way is to put it on for the price you want, and a phone number. Saves a lot of time, if the car's priced correctly it'll sell.