I'm a car dealer, been one for 30 years. I'm an honest seller, and I hate to read these kinds of threads.
Here's what I would do:
Contact the GA DMV and follow whatever procedures they require in order to get a full and complete history (INCLUDING OWNERS NAMES AND ADDRESSES), and contact the previous owners and ask them what they told your seller. I'll bet they disclosed the extent of the damage in a little more forceful terms than he did with you.
Second: Try and find out as much info about your seller as you can. What does he do for a living (don't believe a word he told you). He sounds like a professional "curbstoner" to me (an illegal and unlicensed dealer). He may very well be working with a dealer, he may be a licensed dealer himself. If he's a dealer, there are dealer licensing authorities that will prosecute him for this. I know that GA has some pretty stiff consumer protection laws, but I'm in CA, so I'm not familiar with their specifics.
You could hire a PI to do this, but perhaps there's a local (to him) Mud board member that wouldn't mind knocking on a few of his neighbors' doors and asking about him. Believe me, if he's selling cars, they'll know!
He may be a dealer, maybe not. Licensed or unlicensed. However, curbstoning is very common in all states, and it's a big problem. It's illegal in all states.
If you find the car was traded into a dealership, contact that dealership and ask them to provide you whatever info they may have on the vehicle. Each dealership is different, some may be helpful, others not. Maybe your attorney will get the info.
If you find the car was sold through a dealer-only auction, it's highly likely the car was announced as "frame damaged" at that sale. If he IS a dealer, that's solid evidence he knew.
Contact the GA DMV, get ahold of the arm of that bureau that does dealer investigations. There is such a division, it may be called something different. You want the "DMV cops" that investigate dealers and vehicle fraud.
Ask them to run the VIN, and depending upon the investigator you get on the phone, he may reveal a wealth of information to you. I've had this happen with various personnel at different state DMV's, and some of them are very helpful.
You also should mention the sellers name to the investigator. If this guy has done this before, they may have records of previous actions against him. It's certainly worth asking for.
Do all of these things, even if you hire an attorney. Not all attorneys are created equal, some may think of these things, others may not. You may find a bunch of surprising info about your seller. I'd bet a rusty FJ60 that this is not the first fraud this guy's been involved in. Anything you find out will aid your attorney in negotiations/lawsuits.
Also, what kind of paperwork did you get? I assume you got a title, but was it in his name? At that address? Was the title recently issued (evidence he recently bought the truck)?
Also, you can go online to the County of Monroe GA Tax assessors office and type in his address, get the owners name and contact them to see what he does for a living.
Monroe County Tax Assessor's Office
Good luck, and please do keep us informed.
Dana