If all these people are winner money and its garenteed as you say, where is it coming from, someone is losing money somewhere. Thats just another dodgy scheme like pyramid schemes etc in my opinion, stay away from them, nothing is a sure bet.
listen to alex gardiner, if you have the time to involve yourself in these sort of things, why not focus your energy in the business that you are in.
gerard 
Another one thats making assumptions without reading the link :

Quick very rough example......
William Hill for a new customer have been offering a £200 free bet when you place a £200 bet of your own.
Betfair let you place a lay bet ( a bet to not win)
You bet £200 at W. Hill on a horse/football match whatever takes your fancy.
You then bet £200 on the same race/match at Betfair but as a lay (not to win)
Race/match ends and whatever the result(you backed to win and to lose) you have won and got your initial £200 back.....
W.Hill then give you a free £200 bet and you do the same again... back and lay
At the end of that race/match you get your £200 back and that's all profit.
Potentially £200 for at most an hour signing up and matched betting.
If you want to start at something smaller then Corals do a bet £50 get £50 free.
All legal and above board.
Like I said, takes some getting your head around but easy when you do.