Used-car buyers are being urged to not overlook the vehicle's depreciation when considering a purchase.
Buyers are being advised to calculate the potential depreciation rate by comparing the car's original and current price.
According to guidance, residual values are associated with the age of the vehicle, with devaluation more likely to slow down with older cars.
Nicola Johnson, consumer services manager for used-car history experts HPI, said: "Depreciation can be a 'hidden cost' and buyers who forget to take it into account could be in for a nasty surprise when they come to sell and find its value has plummeted."
Values can be stable or even grow for popular, well-maintained or cult vehicles when bought prudently, according to experts.
Mike Hind, of vehicle valuation data provider CAP, said: "Depreciation is the biggest single cost in owning a car and it can vary massively between brands.
"Understanding what your intended purchase will be worth in the future will help you avoid a potentially costly mistake."
Copyright © Press Association 2011