If you want to be a successful gambler, then you need to flag sports events where the gambling sites have calculated their odds inaccurately. It won't happen very often, and may be you get such chances in 1% or 2% of the matches. Gambling sites have their own methodology to calculate the odds, which may or may not match those of yours. So in case there is a big difference in the odds, you need to analyze the possible outcome and make a bet if the odds look attractive to you.
One example that comes to my mind is the boxing match between Keith Thurman and Manny Pacquiao. Many of the gambling sites provided better odds to Thurman (at least initially). But gamblers made bets in favor of Pacquiao, because they knew that he was a much better boxer.