Let's do some math:
Assuming new tires are $50 each. New chain maybe $20.
Plus shipping for parts you are already at $550+
The unknowns (some the owner may or may not know about)
What about the roll cage? Bearings? Frame? Clutch? Seat? Rust? Shocks? Brakes?
Chances are good that one or more items above need some work/ or replacement. Add $100 for that.
Are you willing to invest $600 plus your time to fix up the kart?
If so, are other comparable carts in good shape going for $600+?
(search in eBay, advanced settings, within 200 miles of your location, sold listings)
The answer to the question is completely up to you.
If you want to buy it, talk cash, and point out all of its problems and your newfound info from above, then make an offer on it.