I know that if you are just working within a small bookmaker or a local one in your place, you are against the Bookmaker, but if it's quite a big audience, you are now against other bettors. The role of the bookmaker there is to adjust the odds and ensure a balance between both sides of a sure bet.
It also depends on the market that you are betting with. I think in polymarket, it's within other players. Based on what I have read, I haven't tried it, but it's a fantastic site.
I also like the polymarket, and it's very strange that no one has thought of this before. At the same time, it's very funny that this site doesn't seem to be fully related to betting, because users don't bet on sports events, but simply on ... events. I also like the fact that the polymarket takes statistics from it, for example, on presidential elections, and therefore we can know the true results of the statistics, which cannot be rigged by interested parties. I know that they have had problems with legislation lately, and I hope that everything will be resolved well.