if it shifts nice and everything is tight im sure its fine. The swap isnt hard to do. If done right you cannot tell it was swapped. Look for rust, neglect, look at oil, Just look all over for anything and everything. Look under it for leaks ask for receipts records etc.
Make sure the body is straight and clean; that all the panels/doors line up, that the subframes look straight, and that there are no cracks in the floor or torque boxes where the rear control arms bolt up.
Mechanically, make sure that the heater core doesn't leak....feel the passenger floor for dampness, and make sure the heat works; replacing those things are a pain in the ass. Make sure the trans shifts well, that it doesn't grind into forward gears (reverse will grind if you don't shift into 5th first) and that it doesn't pop out of any gears while driving. Listen for any peculiar noises from the trans while in gear.
Have the seller start the car (cold engine) while you stand behind the car. When it first fires what do you see coming out the exhaust? If it's BLUE smoke then the engine has major oil consumption issues.
Any more questions, feel free to ask.
if you were seriously interested in buying the car, then i would take it to a shop and have them do the block test, compression test, all the good stuff, to make sure all the internals are working properly, and all the above stated info... listen for those squeaky through out bearings too =)