[elbasti]

Sports betting is zero sum, but the market is very inefficient. So you need market makers (the gambling sites) that will fill any order and that set the initial price.

The correct price is often not known for a short while, and that's when the pros bet. Immediately when the line (price) comes out, if they think the line is miss-priced, they will place large bets.

Eventually the house realizes the mispricing and they change the line, but by that point a pro might have placed a six figure bet.

So pros really are winning from the gambling sites, not from other gamblers.

[cryptonector]

Sounds like this is a self-fixing problem. Either the betting apps/sites will go broke, or they'll get really good at pricing, which will a) push the pro bettors elsewhere, b) maybe bore the problem bettors. Ok, (b) won't happen, but at least (a) should maybe happen. Problem: the betting apps/sites won't be able to hire the pro bettors to help them.