Ok this actually happens to my friend not so long ago, he is going on a boxing match and he will bet for the heavy favorite, then suddenly an unknown guy whisper to him, that the fight is going to be fixed and he supposedly heard it from the favorite to win, locker room, are you going to listen to that and bet for the underdog.
What's your take?
Someone's been kidding obviously
Really, why would you seriously expect a totally random dude to tell you something which, if true, would let you grab easy money? There is no reason in doing this, i.e. the only reason that you can come up with is someone trying to make a fool of you. As the famous (or infamous, depending on your stance) con artist Joseph Weil (aka Yellow Kid) once said, each of his victims had larceny in their heart. So it is the same here with the aim to make your greed cloud your reason and common sense (for the fun of it)