Price: Compare the asking price against other GTOs listed on AutoTrader.com, eBay and in the paper. Look at what private parties are asking instead of dealers.
Inspection: Have the car checked by a mechanic. Check stuff like tire wear, whether or not the clutch is functioning properly, etc. If at all possible, have somebody at a dealership run the warranty service history on the car -- this is extremely important to do. You can do a Carfax, too, but those reports often have huge holes in them.
Known Issues: Here's a link to a list of TSBs for the 2005s, TSB meaning Technical Service Bulletin. These aren't recall issues or anything like that, just a list of notes to help service technicians in the field solve problems more effectively: https://www.gtoforum.com/showthread.p...ight=2005+TSBs
Another thing to do is to visually inspect the car yourself -- taking nothing for granted. Here's a good article on how to buy a used car: http://www.ehow.com/how_2125_inspect-used-car.html
Print this out and use it as a checklist while going around car. Overall, just make sure everything looks good -- and that everything, like the windshield wipers, etc. work. Also make sure there's plenty of time on the factory warranty to work any bugs out if they're there.
While GTOs are great, some have issues where the insides of the front tires rub against the suspension struts. To see if this is happening, turn the steering wheel all the way to one side and look at the inside of the tires and, especially, at the black paint on the strut -- near where the top of the tire would be. If the tire's got wear on the side -- and the strut has some missing paint -- forget buying that particular car as the stupid Pontiac dealers just don't seem to know how to fix this issue. They'll take stabs at it -- but they'll either not fix it or set the suspensions settings up so your tires will wear out in 8000 miles.
My Best Advice: If something smells fishy, be prepared to walk. Never feel pressured or emotional when making a major purchase. If something doesn't seem right, such as your finding paint overspray on a rubber window seal and the seller says "oh, that's normal" just walk away.
If you have any questions, buy all means throw them out. Everybody here's happy to help.