I reckon a deposit is pretty dumb and pointless
seriously $500 dosent weed out the tire kickers from the real buyers.
If u r looking at the $500 as a form of damage insurance...think abt it, if he does crash ur car, its gonna be alot more than $500.
Personally i've driven enough cars to know how roughly all of them feel like. And you dont have to necessarily drive it to know how it feels, sitting in it will give u 90% of the picture, power delivery, handling, and so forth, the only 2 things u cant tell from t he passenger seat is the steering and the brakes.
so just volunteer to take them for a spin round the block should do.