Best bet would be to take it to a mechanic who works on dsms to give it a look over. The short answer is yes, there is a lot to look over before buying a dsm, which probably cant be summarized in a single post.

If you do get it, keep it at stock boost levels, 11-13 psi, until you learn a lot more about the 4g63 platform. I would ask the guy how he tuned the car and look for a fuel pressure regulator - as thats the only way to control the pressure on a 255 pump. If he gives you bs answers, then its probably got some work + parts needed to get it running right.

Also look for strut tower rust and in the rear wheelwells. I always looked up under the dash, just to see if it's wiring nightmare or a fire waiting to happen. Check compression of the motor, while the plugs out look them over. A plug can tell alot about a motor. Also look at the fluids, smell the oil on the dipstick. If you can, have a friend that knows about cars go with you. When I was young and dumb, I had a friend's dad go with me, he was a mechanic and he showed me so many things to look for. Good luck with the buy.

also ask him about the recent service, if any, the car has received. Timing belt, water pump, etc etc