I have bought two cars at Jackson. On the first one, I really left feeling ripped off. The salesmen are like sharks and the financial guy seemed very unfriendly. I ended up spending WAY too much for a cheap car. When I took the car in for service, they told me that they couldn't locate a problem even though a mechanic friend could. That is pretty shady to me.
However, I complained big time and I was pleased with the result. I ended up trading my car in for something bigger and better and I felt I got really good service from the Used Car Manager. He saved my opinion of this dealership.
Overall, I probably wouldn't go back here again unless I wanted a Mercury, in which case, you have no choice it is the only one on the island.