EDIT: upon further reading of this thread I’m just repeating an old conversation so just ignore me.
Digging up an old post in this thread but since I’ve spent 11+ years working in the gambling industry just wanted to say that it is totally legit.
Matched betting works by placing a bet on the outcome of a match to get your free bets, then placing a bet on another site against that bet. Because of the house edge this will result in a small loss, but you then have in free bets that you can use to repeat the process, guaranteeing at least a small win.
Example (all numbers made up off the top of my head):
Sign up to site #1 for an offer of “bet £10 to get £20 in free bets” and bet £10 on Inter Milan to score >1 goal to return £14.
Calculate how much you need to bet to cancel this out, then go to Betfair and bet on Inter Milan to score <1 goal. Based on these bets you’ll lose let’s say £0.45.
However you now have £20 in free bets from site #1. So you bet that £20 on a long shot, let’s say a 5/1 bet. Then, you go to Betfair again and bet £20 against it at roughly 1/5.
If it comes in, great, you have £120 profit and £20.45 losses. If it doesn’t, you have £5 profit. Wash, rinse, repeat across every welcome/reload/lifecycle offer at every online bookie available to you.
Most people don’t do it and even some of those that do don’t do it properly and still lose, so it’s not exactly a huge impact on the bookies’ bottom line. If everyone got onto doing it properly then yes, they’d have problems.
They will still ban people who consistently make profits but because you’re doing it at a multitude of sites then it takes a while. You can definitely make some relatively easy cash along the way.