"when you get on it the car will occasionally blow smoke - JPS response was the and I might get this wrong - but something like chrome moly rings need to seat and this will get better as the engine breaks in - "
OK, so most people on here are recommending you walk away from this.
After 1,500 miles, even with Chrome Moly rings, that engine should be broken in IF the PO broke it in properly. If he was out racing WRXs in the first 1,000 miles of life, then it's probably never going to "break in", period. And who really listens to what John Steele says after the fact, anyway? If the PO did "get on it" a lot before break-in was done, then it most likely has a cracked oil ring somewhere and THAT requires a teardown to fix.
Find a local Suby tuner shop and ask them about it or, if you can find out who built the engine then go ask them about it (and be sure to show them the video of the smoke - that doesn't look good no matter how many miles are on it). The engine may stand behind their product and treat you right - who knows? But you have to find them and ask.
If you can get the guy down $5K or more on his asking price so you can have a decent Suby shop pull the engine, do a tear-down and fix what's wrong, then maybe, maybe consider it because it's gonna cost you $5-$6 grand to get everything fixed and we all know that JPS cars have to be thoroughly gone through after delivery to make them right, if not just to get them safe.
I would keep looking, though.