That is what I was trying to figure out also. Why the #500 deposit????? I would never put any money down till I had a deal and it was locked in. No way before you have a firm price and a deal you want are ok with. With them having some of your money they are in the drivers seat and not you. You just gave them then advantage over you.
I have been to a couple of places and they requested a deposit to show I was serious about buying. Guess what my reaction was, I not only walked from the place I ran. At one of the places the salesman followed my all the way to my vehicle and he had changed his story and now he was willing to try and deal without any deposit money. There is still no way I would ever deal with a slime ball place like that and told him so as I got into my vehicle and drove away.