Obviously if they claim the house edge is 0% they should have some other kind of revenue system for them to make money out of, and the closest thing I can think of is to take money out of players pocket in other forms like withdrawal or deposit fees or maybe their casino website is really not provably fair as the other ones, there are some other ways like those that I mentioned that these supposed 0% house edge casinos can make money from but my suggestion would be to always look for more reputable casino websites instead of looking for minimal or 0% house edge, after all 1-3% house edge which is common among casino websites is not thatt high and it's definitely not worth it for you to risk being scammed to just use a casino with a little less house edge.