As noyb correctly stated they follow betfair odds minus a little percent.(In fact they don't just follow the odds.They are scalping the money you bet, so they earn this little percent without any risk).So I can't say they trick you but they just follow betfair odds... Live odds at Betfair change every few seconds so sometimes they don't accept the bet because betfair odds got lower and the scalping opportunity for them is gone.