If you speak straight to people you don't get comebacks. The punter who wants comeback will be put off the moment you say "it's cash, no receipt, go & don't come back thinking there's a warranty because there isn't".
When I say straight talk I mean STRAIGHT TALK. There must be absolutely no fucking about at this end of the market otherwise you will get comebacks.
Obviously if you're retailing £30,000 German wet dream machines from a big glass showroom this approach is possibly not good for you. The punter on a 3yr old M5 might be somewhat put off to hear you telling a punter on a £300 Focus that "It comes with a lamppost warranty, now either get your wallet out or go cos I'm not fucking about over a £300 banger. Take it or leave it"