Good advice from Trade Vet... We also run a 'warranty' fund at £100. x 250 units (circa) and administer ourselves, last year we spent £13700 and shared the surplus as dividends. Although, as another contributor commented, we are meticulous on mechanical prep. Prevention is better than cure every time.
Plead poverty, tell them the cheque book is closed, perhaps offer sale or return if you need the stock and ,If you are on good terms with your customer(s), get a 'third party' involved who can make them a low ball offer without the wrath of the customer directed at you. Just be careful how you mark the car up on site if he's local.