I stopped taking deposits about a year ago. I run on a “first come, first served” basis and because they’ve not paid a deposit I tell them they’re free to view & walk if they don’t like it with absolutely no pressure. It works 90% of the time because I weed out most arseholes over the phone.
It works for me as I really can’t be arsed chewing on with customers - if they turn up with high expectations they’ve not paid a deposit so there’s no negotiation “Mr. Customer, if you don’t like what you see at my price then please do not get in and drive it, don’t waste either of our time, just leave it to one of the other 63 million of the population”.
Years ago I used to take a £3-500 deposit (it used to concentrate punters minds ), then £200 but nowadays punters seem to think £100 is a deposit (it’s barely a good drink nowadays!) and I didn’t like removing a car from sale for such a paltry amount.