Taken from Wikipedia:
Matched betting is a betting technique used by individuals to profit from the free bets and incentives offered by bookmakers. It is generally considered risk-free as it is based on the application of a mathematical equation rather than chance. A typical return for a matched bet where the stake is returned is 85%+ of the free bet offer amount, and 70%+ where the stake is not returned.
I will be doing the “Matched Betting Made Easy“, Free Bet Challenge with Online Betting School and blogging about it so you can get my views on whether it is something that you might want to do for yourself or not