Which? tested 11 different comparison websites offering insurance quotes and found they tend to make basic assumptions that don't necessarily apply, and may even invalidate cover.
Prices for car insurance quotes varied between £310 and £660, and in many cases excluded optional extras such as legal cover, a courtesy car or personal injury cover.
When it came to home and travel insurance, no single website covered more than a third of the market.
However, if you're aware of the pitfalls to avoid, the sites can still save you money.
DON'T GO FOR THE CHEAPEST QUOTE
Although it's tempting to choose the cheapest option, if it doesn't meet your needs you're likely to end up paying more in the long run.
This is particularly important with insurance policies, make sure you choose a policy that has the right level of cover for you and that the specifications match your circumstances.
ALWAYS SHOP AROUND
Not all companies use comparison websites: for example, Direct Line does not. These websites therefore don't cover the whole of the market, so it's best to visit two or three to get an accurate idea about what products to buy.
Although comparison sites are a good place to research what's available, going to individual company websites as well will allow you to make a proper comparison before you buy.
WATCH OUT FOR SPONSORED LINKS
Some products, such as savings accounts, will be bumped to the top of a comparison table if the company has paid for the position. This doesn't necessarily mean it's the best. So keep an eye open for adverts.