Not a ton of detail in those 12 photos but it looks to be in relatively decent shape. The bayo looks surprisingly good as the coating looks to be intact w/o a ton of flaking which is not always the case. I don't see any huge red flags on this one. It's a C&R covered firearm, so if you have a FFL03 (and live in a free state i.e. not California) he could ship it right to your door & save you the $20 to $40 FFL transfer fee.
I'm not sure whether $600 is a reasonable price for one these days as I've not bought an SKS since 2019. Yugos often get lumped in with the red headed stepchildren of the SKS world as they are numerous, but not necessarily 'popular' like the Russian SKS45 or even a Chinese Type 56. M59s pop up relatively regularly, but if you haven't seen one pop up in a while and have a hole to fill it might be worth pursuing this one.
If you do go for this one, you might PM the guy and see if he will send you additional photos of the matching #'s on the bolt & carrier and any other areas you might want a closer look at. You could ask why he's selling it (is it a problem child?), what the bore looks like (muzzle rifling looks OK from the photos), and how it shoots. For payment, I would *only* use USPS Money Order, never Zelle or PayPal. You have almost zero recourse if the deal goes south with the latter two.