I wonder how much this is affected by the prevalence of leasing. Something like 1/3 of new cars in the UK start off as leases. At the end of the lease period most/all of them hit the second hand market. In this case I think even the seller doesn't know if it's a lemon or not and, in any case, they will always want to liquidate the car as soon as possible, even if it's a peach. So they would factor the market price into the lease deal and sell all cars at market price regardless.