Depending on price, this doesn't look bad. I can't tell if there is any structural frame rust from the pics, but it looks like just surface rust. As for the hole mentioned above, I can't tell if it is one, and more importantly, what is it a hole in? This almost looks like a sheet metal cover and not part of the frame. I've never been under a JK so I don't know what I'm looking at.
I'll say this: If I was in the market for a JK those photos would be good enough for me to go look at it in person so I could crawl underneath and bang on the frame with a chipping hammer and snake the rails with a scope. Those of us in the rest belt won't be looking at frames those in California, Texas, Arizona, etc. They ALL look a bit like this no matter what, unless they are garaged every winter and have never seen salt.