A lot of the 4.7s around here claim to have "new radiators". Does this basically mean it overheated? Should I avoid these like the plague?
The radiators are plastic, which means they crap out over time.
As to if the engine is damaged or not, that depends on how much attention the owner pays. Mine was leaking and I kept it topped off all the time until I replaced it because I was tired of the mess and the leak just got to be too much. That keeps the engine with coolant and thus it's okay as long as the coolant doesn't get so low you get air pockets. Some owners might even replace it right away if they see a leak.
Some others don't pay attention to the coolant or leaks and in that case, the Jeep will warn them they're low on coolant via the EVIC, and when that's ignored, it'll warn them by overheating the engine and leaving you stranded.
The question is, which one of those scenarios happened with that Jeep? And, more than that, I think you'll have a hard time finding a 4.7 Jeep that hasn't had a radiator repair because the things just wear out over time (not that there aren't going to be *some*), so you probably don't have a choice. Plus not everyone is going to bother mentioning they replaced the radiator X number of years ago, they may even just forget.
I guess I just wouldn't worry about it and at least consider a replaced radiator a component that will last you a while longer than a 10 year old part.