IT is probably true in life that being unpopular is profitable and it is particularly true when buying used cars.

You will, I think it is fair to assume, have heard of Vauxhall. But a lot of people have not heard of Vauxhall's Signum. It is like a Vectra estate, but with softer edges, making it far more attractive.

But because no one really knows about it, it is usually £500 less than the Vectra. So a 2007 1.9 CDTI is just £6,400 rather than £6,800, with identical mileage.

The same is true of premium cars, even within one model type. For example, why do hardly any buyers pick the 4.4-litre petrol BMW 6-Series?

Well, because it will cost fortunes to run compared to the more popular 3.0-litre diesel. If you do 12,000 miles a year I calculate about £1,000 more.

But, the thing is, if you buy a three year old one, it's at least £6,000 less than the diesel to buy. Which means it will take six years before your fuel bill outweighs the saving on purchase price.

With used car buying you have to be so careful about conventional wisdom. Bucking the trend can save a fortune. It's finding the trend in the first place that can be tricky.

For example, with most makes you will find the average retail price of a used diesel is more expensive that the equivalent petrol.

Yet with Ford it is the other way around. This is probably due to the high volume of fleet sales that they make on new cars, which in turn generates a lot of nearly new used cars. And lots of supply will always soften prices.

If you are focused on buying the best value car, rather than a particular make, the best advice I can give is to go to the various websites (including UsedCarExpert.co.uk) and search purely by budget in the ‘for sale' section.

A quick cross check with the stats section for miles per gallon and insurance group figures and you will find opportunities at almost every click.