As a fellow EOC member that JUST bought a SOP 04 from someone on Craigslist last week, I have a few tips for you that you may already know, but it's worth repeating.
1) Get a Carfax. You never know where this car was, who owned it, was it a salvage title, flood damage, millage reporting problem, etc. It's a piece of mind BEFORE checking the car out. If the carfax doesn't look good, don't even bother.
2) Don't trust the Carfax. I just mentioned that the first thing you should do is get a Carfax. However, I have seen numerous times that small accidents, fender benders and even big accidents were never reported to Carfax.
3) During the test drive. Question everything. Trust your instincts. If things look too good to be true, question yourself. Why is the engine bay dirty/clean? Drive it hard and brake hard so you can see if the car pulls one direction. Do the rolling down windows, fan checking, speakers after the test drive.
4) Bring a Mechanic. Unless your an autobuff, bring your mechanic to have a second look. There's almost NO need to bring them if your buying a new car, but for used, they are your source of truth.
5) Find things to negotiate the price. New tires, brakes, cracked windshield, etc are all things that can bring their asking price down. Maybe your mechanic found items that need to be changed.
Good luck on your search. I was real fortunate to find my SOP within a few weeks. If this one isn't it, there will be plenty more on the horizon. Let us know how it goes!