[martincmartin]

An economist literally won a Nobel prize for answering that: https://en.wikipedia.org/wiki/The_Market_for_Lemons

When you buy a used car, even one that's less than a year old, you have no way of knowing if there's something wrong with it. So buyers offer lower prices. Then a seller who has a car that they know is good says "I'm not selling it for such a low price, I know it's worth more." So the only people who sell used cars are the ones where something is wrong with them. A kind of race to the bottom.

[globular-toast]

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.