There was a topic along these lines last year I think. The problem is that every bar you are advised to avoid has many fans too, so you get "Don't go to ***** Bar" followed by 26 "You don't know what you are talking about" replies. Also people generally tell CBF which things they love, they tend to dislike on a far more private basis, which isn't likely to change.
I may be wrong but my experience tells me that when someone goes to great effort to smear a bar or restaurant on here, it can usually be traced back to a personal vendetta or fall out rather than any fact or facts worth hearing. There are bars and restaurants I don't like and I choose to go to others instead. At the same time, I am aware that they have their happy regulars too.
Rip offs you need to know are the clothes shop change guy, the old git who clasps your shoulders without asking for 2 seconds then demands 20 lira, and anyone who sells Efes as a career and houses because you are "special friend".