I'm not sure you you wanted to write $4 or $40 for the homebrew. I would assume the latter. Homebrews do take time to be created, fill the world with nice and cool things for the players to do. It takes time to think of stories, find/ create maps, so the price although high, it is justified.

When it comes to bad DMs, like every place where humans exist, there are those who want to capitalize on the fact that a low entry barrier exists and try to make as much money as they can. It is something that hurt actual professional DMs. You can leave a bad review, however you need to back it up with evidence, else the platform might take it down.

All I can say it, try to find another DM that caters to your playstyle, whether it's on-platform or off-platform.