Question about sports betting "freeroll" strategy

[hmkpoker]

I'm completely inexperienced with sports betting, don't know anything beyond the basic mechanics of the spread.

A friend of mine told me that there is a strategy where you simply find two bookies (out of god-know-how-many) who are offering odds that, together, create a positive edge for the player, so if he bets a certian amount on both, he can't lose.

Does this actually work? Or are all bookies so close together in terms of the spread odds that this strategy isn't profitable?

(If this is true and well-known, I apologize for sounding like a dork since it must sound like "can someone really beat poker in the long run," but I couldn't find the answer via search and thought I'd ask.)