WE SHOULD all know the drill by now. Something happens - an interest rate cut, say, or maybe an energy price rise – and before you know it all and sundry are telling you the only way your wallet will survive the impact is if you switch all your products to a new provider.

How do most of us search the market for the best deal? Through a price comparison website, of course. But how can we be sure said comparison sites are really showing us the best deals available in the marketplace and, indeed, how to we compare the comparators?

A simple search for a cash ISA highlights just how different the results can be across sites. On MoneySuperMarket, for example, the top result is a product from Skipton Building Society that pays an interest rate of 0.9 per cent while on Gocompare, once the help-to-buy ISAs are stripped out, the best rate, at 1.95 per cent, comes from Principality Building Society.

On comparethemarket, meanwhile, the best cash ISA rate is on Ipswich Building Society’s Stepping Stone ISA and comes in at 1.55 per cent.

Similarly, a simple search for a zero per cent balance transfer credit card throws up different results across the sites, with a Barclaycard topping MoneySuperMarket’s list, one from the AA coming top on Gocompare and card from Halifax on top of the list at comparethemarket.

According to the Competition and Markets Authority (CMA), which is mid-way through a large scale study into what it terms the digital comparison tools market, “there appear to be areas where sites could improve transparency, particularly around their market coverage, business models and ranking methods”.

“Competition needs to be effective, both among digital comparison tools and between them and the suppliers whose services they compare,” it added.

While this means that consumers keen to search out the best possible deal should spend time searching numerous comparison sites rather than relying just one, Personal Finance Society chief executive Keith Richards said that for more complex financial needs even wider searches could prove inadequate.

Noting that comparison sites have “created an environment where consumers can feel more engaged and aware of their personal finances”, Mr Richards said they can also lull consumers into a false sense of security when it comes to making the right decisions for their circumstances.

“Many sites do not necessarily cover the whole of a market and they are often analysing complex markets that simply don’t support a one size fits all approach,” he said.

“For example, in the mortgage market, there are so many subtle differences between lender offerings that these cannot be accurately represented within a price comparison tool.

“Administration charges, arrangement fees and other mortgage costs are difficult to compare, let alone specialist lending products, later life lending and equity release, which in many cases are an important consideration for borrowers.”

The good news is that, while the comparison sites do not offer full-market coverage, most people who use them seem to know that and few seem to mind.

In its study of 4,000 consumers, the CMA found that while just 11 per cent thought they were seeing all the deals on offer on any given site, over 90 per cent were satisfied with the site they used.

“Furthermore, most users, but also a substantial proportion of non-users, believed that using digital comparison tools led to, or would lead to, better choices,” the study said. “Two-thirds considered that the results on the main site they had used fully matched their needs, with only two per cent saying that they did not match their needs at all.”

Indeed, the CMA said that comparison sites “can make searching around and switching easier for consumers, and can encourage disengaged consumers to shop around when they otherwise might not have”.

“Shopping around and switching can directly benefit consumers, but they also strengthen competition,” it continued. “Digital comparison tools can also make it easier for new suppliers, particularly smaller ones, to enter the market.”

Understandably, the comparison sites were quick to seize on this, with MoneySuperMarket editor in chief Dan Plant noting that the CMA’s findings are “broadly positive” while Gocompare chief operating officer Lee Griffin said the study shows “that digital comparison tools, including price comparison websites, stimulate competition, increase consumer choice and help people make informed decisions on a wide range of products and services”.

While this may be true, for Mr Richards nothing can beat the security that comes – at a price – from taking expert financial advice.

“Consumers should be encouraged to utilise the online tools that are available to them, but this should be complementary to advice from a professional intermediary, whose full-time job is to investigate the myriad of products in their market and align them to the specific needs of the client,” he said.