It said dealers were braced for large numbers of trade-ins as the market hits the Easter holiday period.
Values already lower than a year ago will come under increased pressure and some used car retailers were already fully stocked ahead of the Easter break, it said.
Cap said the market was increasingly polarised with ready to retail cars fetching “unsustainable” prices while secondary stock requiring remedial work languished.
Black Book Live senior editor Derren Martin said: “Dealers are particularly vociferous in their complaints about the relatively high values of the best quality, low-mileage, and cars at present because margins are under sustained pressure.
“But at the same time lower quality cars, for which there is less demand in the trade, cost time and money to prepare for retail presentation – and that eats into their margins too.”
Martin said there was no risk of a market meltdown.
