Next time you decide to ask a car enthusiast what your car is worth or what you ought to spend on a car, tread with care. Many of them know less than you (or they) think, according to a new study by Carbidder.com, the new online used car sales and auction site.

The company researched over 1000 car owners. Of these 17% said they were good or excellent at getting a great deal when buying or selling a car -this rose to one in five among the men studied. 21% had been to car auctions and 26% said they had a good or excellent knowledge of cars – again rising to 36% among men.

Yet when these same car-savvy enthusiasts were asked to value four different second hand cars, either as a buyer or seller, few displayed the talents they had described.

The cars they were tasked with selling were a 1999 Volkswagen Golf GT TDI and a 2002 Peugeot 307 5 door hatchback. Both cars were in good condition, had full service histories and average mileage for their ages.

In both instances the participants vastly underestimated the prices the cars would secure in private sales. A massive 91% overall undervalued the Volkswagen Golf – a third reckoning it would fetch just £5,000 to £5,500. In fact in a good private sale, the car would fetch around £7,600. Even 58% of those who said their knowledge of cars was excellent, underestimated its sale value – and half the ‘good dealmakers’ in the study would have not secured its proper price if they had been driving the deal.

Similarly with the Peugeot, just 11% of those who said they had a good knowledge of cars correctly estimated that a good private sale price for the car would be around £8,400. A massive 58% were more than happy to accept far less for the car.

As car buyers the group fared little better. Asked what they would pay a private seller for a BMW M3 Convertible almost a third would pay more than £15,000 – the car’s good price at a private sale. A fifth of those who said they are excellent at getting a good deal would also pay too much.

The experts found it easier to put a price on the Renault Megane 1.6 hatchback – with 18% getting it right – but again 44% vastly over estimated its worth.

Selene Regan, founder of Carbidder.com isn’t surprised by the findings: “People find it incredibly difficult to judge cars - especially when put on the spot. There are so many factors to consider – and it’s quite an emotional subject too – some people will simply pay that bit more for a car they really like.”

According to Selene, it is through this emotion that great deals can be made on auction sites like Carbidder.com.

“Someone selling a car through a site like ours can fix a reserve price. That way they know they are going to get the minimum they want…but they also know that if their car catches the right buyer at the right moment, they could walk away with a fantastic sale price. Equally we have seen buyers come to our site and secure an unbelievable price on a dream car. It’s this thrill of a potential great deal which is driving traffic to our site.”

Carbidder.com’s research bears this out. Over 45% of the 1000 car owners studied said that the biggest advantage of buying a car online was that you could get a lower price, 21% said you could bargain more easily, 43% said you were offered more choice and one in five said you could get a good deal.

To help sellers and buyers value their vehicles prior to listing or bidding Carbidder.com features a paid for online Glasses valuation service. As a special offer, Carbidder.com is offering a free Glasses car evaluation voucher – worth £2.95 – to the first 400 people who place a bid for a car on the site.