That laptop is overpriced. For $879 + tax you can order a new 15.6" Lenovo Y510p which comes with a current generation quad core i7-4700mq and a nVidia GT 755m. Both are more powerful than the CPU / GPU in the used Asus. The performance of the GT 755m is between the GTX 560m and GTX 570m. Since it is new, you also get a 1 year warranty.
http
/shop.lenovo.com/us/en/laptops/ideapad/y-series/y510p/
It comes with 8GB of RAM, but it is easy and not very expensive to upgrade. But that is enough to play games with.