Check the kbb and compare. I would still negotiate on the price in case things like the lim, elbows etc need to be done. It gives you some wiggle room for potential repairs.
bigger question is is this the original owner? and was the tranny ever serviced before. owner seems to be claiming he keeps up on the maint, so maybe hes a good owner and had it done 50,000 miles ago, if so thats ok that he flushed it.
its when its never had a service in its life and its over 100,000 miles your asking for trouble. but then some times if it wasn't beat on, aka adult owned, the fluid may have been in good shape when he had it flushed.
http://www.grandprixforums.net/thre...-guide-Common-problems?highlight=buyers+guide
this thread covers it all pretty much.