The 92G was sold to law enforcement only, and the Blue Book states it is valued slightly higher than the 92FS.
It is hard to say without seeing the pistol, but a 92FS in 70 to 80% condition is valued at $300.00 to $330.00.
As I mentioned in another tread, I have no idea what the recent turmoil is doing to higher capacity pistols prices.
You might want to counter with the above $ numbers. Good LUCK with it.