Vegas doesn't exist as a desert oasis simply because they can guess well. Vegas KNOWS.
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"Does Vegas adjust the lines based on the known betting habits of certain fan bases? They almost certainly do, but I have never been able to detect any clear bias in the data. Also, it would certainly be very easy to do that for just a handful of games, and that data would just get swamped by all the other data. So, I just ignore this possibility. If I can’t measure it systematically, I don’t care about it.
Practically, if a team is favored by 10 points, this translates to a ~75 percent chance of victory for that team. Does this mean: If those teams were to play 100 times, one team would (roughly) win 25 times and the other would win 75 times? OR, does it simply mean that in any given game with a 10-point spread, the favorite will win 75 percent of the time by an average margin of 10 points. I think that the second statement is clearly the correct one."