alt Hacker NewsBets with a positive edge can be found most commonly via sports betting, poker games, and the stock market. Although note that most bets you can find via such methods do not have a positive edge, and the edge is not labelled.
More generally, look for any area where bets can be made, and professionals exist who make their living winning such bets. There are professional poker players and sports gamblers; there are not professional roulette players.
The problem with sports betting is that if you really want an edge (at least in something like soccer) you could easily end up dropping six figures a year on data licenses to have a decent model and be able to find worthwhile bets across all competitions. That puts a lot of pressure on the amount of capital you need to deploy, which rules out a lot of bookmakers. As you graduate to markets with more liquidity (i.e. Asia) you’ll also find your edge shrinking. Still obviously very doable, but it’s hard to guarantee stress free passive income this way.