House edge is the only avenue where the gambling industries are using to make their own money, though this charges varies from websites to websites and the percentage also differs however 0% house edge gambling site should not be trusted because they will eventually scam you.
I dont agree with you that gambling sites that does not have an house edge are a scam.
Some gambling sites offers a game with no house edge to attract some gamblers, and they make their money from other games that are available on the website.
Also betting predictions sites are also available, where you bet against other people with no house edge.