The three chronic rust areas on Scorpions are:
1) Underside of hood around the vents - it's a bear to fix this as it's a double-layer construction with water absorbent in between
2) Bulkhead behind the seats - rear window will leak behind the seats and make a mess of the bulkhead and the floorpan(s). There's this foam and tar soundproofing which also absorbs and holds water against the fine Spanish steel underneath. Getting this crap out is a pain in the butt.
3) Engine compartment under the heat shield above the muffler-shelf
If the seller will let you get intimate, check these spots. The most difficult to fix is the hood, the most tedious to fix is the bulkhead. The engine compartment is pretty easy, but will be a surprise when you see it. Ideally, all of this has already been done.
Rust aside, broken seat backrest is also a common problem in these cars if the original seats are still there. The rear taillight panel is also very easy to break, and next to impossible to source a replacement. Be sure it's there and fixable, or prepare to make a new one yourself.
All the other usual X1/9 stuff worth a check too (bushings, ball joints, bearings).
Sloppy shifter is an easy fix usually - these nylon cup things fall out, easy to obtain, tricky to install but it works fine.
Get to know the folks at Monte Hospital - they're the bee's knees.
http://www.montehospital.com/