For what it is worth, I own an 83 which was manufactured in 1994. As i understand, they were manufactured until 2012 and not due to lack of demand. I have had to replace the extractor and its spring twice and the recoil spring once. I have also had to replace the magazine followers as they eventually wear and chip away where they interact with the slide. Also, I had to purchase new parts for the magazine release as they tend to wear and I don't think it is the best design. Not too bad for 20+ years of use.
When I bought mine in '95, it came with 1 10-round magazine which is obviously different than the 12 rounder you referred to. If the magazine it comes with has a seam on the front and rear and says "CZ MFG" on it, it is an aftermarket mag and may not work reliably in the pistol. The pistol shoots great when everything is working, when your springs, mags etc have some problems, then it can be frustrating to find and fix the problem.
P96 is right about the replacement cost of reliable OEM magazines and how good the internals are.
I think $349 is high for what you describe. It makes me think that he bought it for between 250-300 dollars from a surplus dealer and is trying to flip it and make some money.