Been researching markets and I'm curious which cities have you tried flipping in that just didn't pan out?

We all hear about the hot markets where everyone's crushing it, but I want to know where you wouldn't go back. 

Slow sales? Rehab surprises? Permits taking forever? ARVs that looked good on paper but fell apart? too much competition, thin margins, holding costs eating you alive?

Trying to learn from the trenches before I pick my next spot. Where would you personally avoid and why?