If I agree to purchase a new car today on PCP and the car has a delivery/build time of three or four months, must the dealer now, at point of ordering, give me a firm price for my present car - or can he give a likely estimate but say that it might change when the new car is ready, due to changes in the market value at that time? If so it seems strange that the future car is already costed but the exchange car has to take the luck of a future market. Any knowledge of how to play this?