Tipsters or sports betting prediction sites exist for the lazy or novice gambler who wants someone else to do all the research and work behind betting successfully. Whether the tips works or not is not important. The money for the tipster is in selling the tip.
Expected value is the means whereby you'll discover whether a bet is worth taking or not. Once you can calculate this, then you can bet where ever you find value, even on the losers. Remember that you're a for-profit bettor and this is another toll for your arsenal.
Sports betting is very different from casino games in one very important factor, namely, there's no fixed house edge, whereby the casino can take a fixed percentage right off the top of every bet. To that end, if you want to be successful at sports betting, you'll need more than just plain luck. You'll need some skills. So in some ways, you could almost compare it with poker or blackjack at the casino.