Watch out for.....
The number one issue by far is RUST. Don't even think of buying one that's been in snow/salt country. Ferrari uses lots of small bolts and nuts (4mm). You'll break them off and be really sorry. There are so many 328s for sale from California, Arizona, Nevada, and other dry climates that it's not worth messing around with rust, at any price.
Other than that, most of the cars I see have oil leaks. I HATE oil leaks, but they are fixable. Trans shifter shaft seals are a weak spot, but doable. Make sure you try out all the transmission synchronizers. All seem to be stiff going into second gear when cold, but should smooth out once warmed up. If not, you can expect a huge repair bill. Weatherstripping is easily available, but quite expensive, if you choose to replace it. Make sure you get a good maintenance history on the car, especially, of course, on the timing belts. The belts themselves are cheap, and can be replaced in the car. Valve adjustment is tough to do, but is possible. If the belts and valve adjustment haven't been done recently, deduct a bunch from the price you are willing to pay. Let's see, what else. Try out the heater controls. There are separate controls for driver and passenger. Each has a small control panel that cost several hundred dollars to replace if defective. Air conditioning seems to lose charge, but is no more difficult to repair than any other car.
Don't forget that these cars are 17 to 20 years old. Every gasket, seal, and hose probably needs to be replaced, even if the mileage is low.
That's all I can think of off the top of my head. Just remember, every thing is easy to fix except rust. If I think of anything else, I'll let you know. Where do you live? -Steve