Here is what I see and know based on my current experience fixing a rusty jeep. The first pic of the torque box / body mount is a potential landmine. These also rust from the inside out and the slight bulge evident in the pic is a tell-tale sign. They may be solid today but guaranteed they will need attention if you plan on keeping it for any length of time. I would ask for pics of middle and rear mounts for both sides of the vehicle AND pics of the frame-side of these mounts. Two repair options- replace the full torque box or have rust cut out and shorter c-channel patches welded in. Obviously the first is the preferred method. Both are labor intensive but not necessarily hard for a typical shop. This would easily drop the price a couple grand for me. The pic with the muffler hanger is also a potential issue. I am at work and going from memory, but I do not recall a welded plate under my frame in that area and it looks like there is one in that pic. Sure sign of a crappy frame repair if someone randomly welded steel under that portion of the frame. It likely means that portion rusted through and that is how they 'fixed' it. If that is the case, that would also be another couple grand. There are also aftermarket frame caps that can be professionally welded in but remember that this type of repair, even if done properly, will reduce the value of the Jeep, particularly a Rubicon. Again, just my opinion, but unless I was getting it for under $10k, I would walk. If you can afford $15K, it sounds like from others more knowledgeable that there are much better ones to be found.