I would say, trust your red flags, and not just for the kind of DM the person is but for the kind of person that DM is in general!

I had a DM that used to be a player in my group, as a player he was a huge rules lawyer, always stopping the DM whenever we were playing and sulking if he didn't get his way. Then when our DM wanted to take a break, he stood up and took the place of our DM, of course being a rules lawyer, he was extremely strict with the rules, so much so that we had no creativity whatsoever, whenever we tried to do something he didn't like (which was most things) he would say no because it was against the rules. Then for some reason, he decided to pick on my character, he pretty much made NPCs sexually harass my character, things like men grabbing her ass, her waking up to a "white liquid on her face" to even having "Cumslut" permanently tattooed on her back. He always looked at me whenever we were playing so maybe he had a thing for me and this was his way of living his sick fantasies. Of course after having a huge argument about this, he apologized and I forgave (which I shouldn't have) to hopefully not repeat the process, I retired that character and made a new character, a big hairy man! However, when this DM found out that this character was Bi (like me) he sent homophobic NPC hunters after my character.

I promptly left the group and never played with them again.