Entertaining the idea of a new car purchase is an upper-middle class thing, and a fully-refundable $100 is impulse buy territory for most of them. Yes, many of them would have been capable of taking on a $40K purchase, but $100 is not a serious indicator that they were serious about doing it. People who have this money are doing relatively well and blow $100 on much more inane things that aren't refundable.

A traditional dealer would ask someone with much less money looking at a used Nissan Sentra to put down $500 to hold a car.