What Nester says is exactly right.
If the rear spring shackle mount is bad the fix can be as easy as reinforcing the frame or cutting away the bad and re-boxing it. I just had to reinforce mine on my '86.
But in the case of this '84 CJ unless he has the equipment and knowledge it is going to be a costly repair.
If you look at the pictures of this frame closely you will see it already has had a plate welded on the under side of each frame rail, this is only a temporary fix. In the pic you did not post of the other side you can see where the spring mount has gone through the frame !
My Tip. Tell your friend to steer clear of this one unless he is looking for parts and a drive line.
The seller of it probably bought this w/o knowing the true condition of the frame and took it off road or even hit a pot-hole and punched the spring mount through the frame. Now he is trying to recoup his loss because he didn't plan on the repair.
Also from the Pics you can see they have not shown any inside shots of the tub, I'll bet this tub has many patches or bad body mounts so the tub is most likely scrap too.
With E-bay you have too look at what your not being shown. 'Cause if it's something good you'll see more pics of that to distract you from the bad.
My final thought: Frames usually rust from the inside out, to repair one best you have to cut all the way back to what is good and replace it. Even if you sandblast the outside and plate over the holes it will continue to rust on the inside thus eventually rusting through where you added new metal.
Pass this on to your friend glad he sought out advice when there are still 5 days left on the auction. Hope this helps