It is warning fleets that residual values on luxury cars could fall by as much as £1,000 if the service history does not come from the same provider.
Once block exemption reforms are introduced in October this year, fleets will be able to service vehicles from a number of outlets, not just from the main dealer network.
Jeff Knight, editor of CAP Monitor, said that for ordinary vehicles, having a full service history from the same provider is not the issue it is for luxury vehicles.
He said: 'When prestige vehicles enter the disposals arena the buyer will continue to view service stamps from the originating dealer network more favourably. This is a function of the perceived sophistication of cars at the higher end of the market, along with the fact that the more exotic a car is, the more specialist attention it requires.
Non-manufacturer service histories could reduce the value of a car originally costing £35,000 or more new by up to £1,000 and more for higher end models.'