The sites work by paying cash rewards for people who click through them to buy products, with retailers paying the companies for bringing in customers and firms passing on a percentage of that commission.
Research by consumer group Which? found using a combination of credit cards and websites, a couple booking a two-week holiday could save more than £300 - equivalent to 11% of the cost of the trip.
Which? editor Richard Headland, said: "We've found cashback websites can save hundreds of pounds off the cost of holidays especially if you book with a cashback credit card."