“Optional extras simply make the car easier to sell,” said Paterson, “They don’t necessarily improve values.”

According to CAP, a more expensive model variant offering better standard spec is better than loading a cheaper version with optional extras.

Mark Norman, CAP’s head of automotive intelligence services, said optional extras typically retain no more than around 20% of their cost, compared to around 90% of a better equipped derivative.

Online advice

Factory-fitted satellite navigation, for example, can retain as little as 11% of its original cost after three years.
Just as the options list grows, so too do the sources of guidance for used car valuations, aided, as ever, by the internet.

Both Glass’s and CAP have been busy refining their online services, driven mainly by increasing market volatility, but also a recognition that just as customers go internet shopping for a replacement car, they’re also likely to key in the registration of their current model to get an idea of its trade-in value.

Said Paterson: “It was on the back of research showing that 90% of the public overvalued their car that we introduced the Glass’s certificate service to give them a more accurate assessment.

"They have the confidence of knowing that this is an impartial value which they can show to the dealer as the basis for negotiation.

“They’re not wasting the dealer’s time with unrealistic expectations. It’s created more of a level playing field. ”

Wright takes a more sceptical view. “Websites like ‘we buy any car’ cause a problem because they give inflated values.

"Maybe that’s because the seller is economical with the truth or light on detail (when keying in information). It places extra responsibility on us to explain why we can’t meet their expectations.”

Added Smith: “Consumer valuation sites are not actually in the business of selling used cars. Typically, on older models you’ll have someone expecting £1,200 to £1,500 whereas in the real world it’s worth £800.”

As part of a programme revamp designed to improve the accuracy of valuations, Glass’s is moving from a one trade value for any vehicle to three condition-based values used by auction houses and more refined mileage adjustments.

Developments this year include more frequent updates and valuation of vehicle options through direct access to manufacturer databases.

Glass’s will continue to value options separately, saying this is especially vital for premium brands.

All the changes, due to be introduced in late summer/early autumn, will be available through GlassNet, Glass’s online valuation tool, and other digital products including Evaluator.