If our specialization is good, probably know more about it than 90% of bettors to the event, and possibly more than we control also responsible for setting quotas. That we must take advantage. One of the "reasons" (to name one) that usually count as an excuse for a value bet is that a team has started a competition with a run of results, but those results were produced against far superior opponents therefore, to play against opponents of their level contributions may look "too" affected by these previous results and there exists a good prognosis.
The odds maker will set fees in order to secure benefits for the bookmaker, often knowing that they are not well placed. Of course, many people (losers) play with bad bets or just for fun even giving away the money, so these losers promote the existence of good bets.
Returning to the previous example of a team with poor run of results call him Team B), we would say that his opponent (this time on your level, we will call C) minimum quotas will have very bad. The losers or bad bettors (which are many) will insert money for team C, arguing that the defeat of B will again, almost certain. As this fee is very bad, by default, the B team victory because the share value will be higher than we expected.
Controlling these factors through experience, many times we are able to derive possible value bets even before the quotes come to light, and remember, the odds makers are not stupid. Just play with the quotas for bad bettors bite into them like a fish on a hook, thanks to them value bets exist, hence the phrase that they feed losers to winners.
A good tipster, or one with experience know which forecasts can find value even without looking at the odds for each event. Easy, just trying to find some characteristic, some news, some peculiarity that makes us go against the market or at least, not so in favor of the possibilities provided by the event manager odds maker.