Used car haggling

I`ve been looking for another car for several weeks now and just recently found a car that appeals to me. Unfortunately it`s at a dealer, which means I`ll have to prepare for hours of back and forth haggling with a salesman. I know I`ll hear all about Kelly Blue Book value and all of that BS so I`m wondering what`s a good offer to begin with ....10% off the sticker? I`ve checked Edmunds "true market value" and the car is well above it, but after looking around it seems like everybody is well above TMV. Any advise would be appreciated.