I'll throw in my $.02. I'm from the northeast and for the life of me I can't imagine why someone living in California would even consider a jeep that had ever lived in a place where they salt the roads, assuming that is where this one came from.
Anyway, if they've painted the frame you need to get under there and take a good look to see if any weld repairs were done on it. Often you can see where frame caps were welded on. Look where the tranny/tcase skid plate bolts to the center of the frame, look where the rear track bars mount. Stick your finger in any holes it'll fit in and feel around for rust and scale, it should feel smooth. Even better get a borescope and feed it through the frame and see how it looks. Also, the rear crossmember where the shocks bolt to is in a nice area to get plenty of salt spray and is often crusty, so make sure you look at that. Take a screwdriver and poke the bottom/lower sides of the frame in the areas discussed. Taps with a chipping hammer are better but some people don't like you pounding on their frames. Take your time. If all that pans out, look at the channels where the body mounts to the frame and poke/tap on them as well. Look at the floors and generally all over the bottom of the body. Some issues in floors wouldn't scare me as they are pretty easily fixed and not a structural problem, but avoid any of this if you can (and you can, you're in Cali). If all that pans out Look carefully at the front fenders between the hood and the plastic fender extension. In the rust belt, the front fenders rust out like crazy in these areas. Look for rust, or evidence of bodywork. Also in the rust belt areas the windshield frames often rust out. This can usually be seen from inside the cab looking down over the dash to the bottom of the frame. If it's gotten bad enough, you may see a hole(s) here. You can't see where it starts, which is at the bottom of the frame without folding the windshield forward and they aren't gonna let you do that.
So, that's where I start looking for rust. There are plenty of mechanical things to look for too, but for me, if I find one that is pretty solid structurally and a good price that's the key.
BUT!! Again, you are in California. I wouldn't even consider one that came from a rust belt area. Be patient, take your time and keep looking. A lot of us have looked for months and months for the right TJ. In my area there is a LOT of rust bucket junk ones, and the ones that are in good shape command top dollar. Also, consider expanding your search, maybe Nevada, etc. I wouldn't want one that had played on the beach too much either.
Good luck!
Edited to add that with this jeep, with these particular pictures, none of us can offer much of an opinion. We would need detailed pics of the underneath. Even then, you need to do your due diligence and spend the time crawling around underneath it. It sure looks pretty on the top, but I've looked at MANY low mileage TJs that looked perfect on top only to find scaly nastiness on and inside the frame.
