How accurate are Vegas odds in sports betting?

More accurate than you might think. Just look at odds on college football. Ever see a college game where the spread is 2 1/2 and the over under is 74? And the final is 38-36 in Triple Overtime? 

The odds or the spreads?  

More accurate than you might think. Just look at odds on college football. Ever see a college game where the spread is 2 1/2 and the over under is 74? And the final is 38-36 in Triple Overtime? 

It varies by proximity to the start of the game, the type of wager, the sportsbook and the sport, but in general pretty accurate. The closing lines at Bookmaker / BetOnline / Matchbook / Pinnacle are the most accurate. The opening lines set by the actual oddsmakers at early books are the least accurate, which is why the max allowed wager is smaller when the line first opens and why there's line movement between then and the start of the game. Prop bet lines are less accurate than spreads, moneylines and totals.

There usually isn't a ton of line movement, so the available edges to gain are small, especially as you move up in stakes. A bettor's goal is basically to lock in a wager at a price that turns out to be better than the vig-free closing line at the sharp books. Any time you do that, you've most likely made a +EV bet. Bear in mind that when betting a spread bet laying -110, even if you make a +EV bet you're still only 53-55% to win (ignoring pushes) unless you got an exceptionally good bargain (eg you already bet on Team A and then Team B's QB got hurt in practice, moving the line 7 points). So anyone telling you about "locks" is probably clueless.

They are perfectly accurate.

If the odds say you need to bet 150 to win 100 on the favorite... then that's exactly what you need to bet if you go to that casino.