I don't think the sites that give / predict the results of football games work much, I think the best strategy is to follow the performances of the teams closely, games won, player shape, injuries...
Absolutely this. Don't trust these websites, they are absolute garbage. The best you can do is your own research. It's like always, if you prepare and do research you (might) win, if you blindly trust some random website who claims to know the final results you will lose on the long run.
If someone would know how the final result of a game is, why should this person share these essential information with the public? He could better just place some (high) bets on some games and win big himself.