Back in the 1990's, some importers of surplus SKS rifles were advertising some of the highest quality SKS's as parade rifles and charging a premium for them.
They reportedly had nicer bluing and stock finishing.
I think that one of these premium guns would be worth paying a premium price.
Since those premium "parade" SkS's may have cost an extra $50 back in the 90's, they should be worth close to the extra $200 today.
At least you know what you're getting.
Some individual guns are simply better & more desirable than others.
Personally I would not buy that one on Gunbroker for $600, especially if there were a mint unfired one available, even if it cost $800.
When I see a gun at a gunshow that I'm on the fence about, I try to get his business card or contact info. so that I can contact him after the show if I decide that I want to try to buy it.
I'm curious if you did the same?
He may accept a close offer for it if you wanted to haggle a little over the price.
Unless you want to watch or attend a lot of gun auctions with hopes of winning a similar USSR SKS for a lower price, you may never see as nice of an SKS for a much lower price than that.