The Yugoslavian SKS is a well built rifle,they tend to be about 1 1/2 lbs. heavier that the Chinese or Russian SKS because of the heavier bayo,grenade launcher and sight. The main thing to look out for on the Yugo's is the gas selector button make sure you can depress the button and move the selector back and forth from single shot to semi-auto fire easy.
The Yugo SKS rifles had corrosive ammo fired through them during there military use so it wise to inspect the bore and the gas block selector switch for corrosion from improper cleaning. Other than that just go by the standard you would when purchasing any other rifle as far as fit and finish.
The Yugo rifle can come in a couple different conditions issued which is just cleaned up and put back in storage usually these are in worse condition,unissued have been factory refurbished,you can determine this by looking on the heel of the hand grip there should be a square with a #2 inside it. Then there is always the new in box or NIB pretty rare these day but there out there.
I have a 1970 unissued Yugo M59/66A1 although the gas valve looked perfectly fine it would not eject some wolf X39 ammo but it would any other mil-surplus or American ammo or my own reloads. The gas valve problem is a simple fix a new valve is available for around $10,I replaced mine at it solved the problem with the Wolf ammo stove piping. I pretty much avoid wolf X39 ammo anyways now days since I reload. Of course being your in CA the grenade launcher will be remove and replaced with a muzzle brake.
My 1970 Yugo
My brothers 1987 NIB Yugo never fired