If the rear end is shifting around, something is broken, installed incorrectly, or loose.
There is nothing on an 88 (especially) that should allow that. There are not even any bushings in the cradle. It's solidly mounted to the space frame.
It's possible that the strut bolts are loose, and allowing the knuckles to shift around. That would be a "best case" scenario. Anything else will be a bunch more trouble. (I'm thinking bushings or structural stuff.)
When he mentioned "tire kickers", you should have countered with "scam artists".
To directly answer your question...
Before I figured out what was going on with the rear end, I wouldn't buy that car at any price.
[This message has been edited by Raydar (edited 12-11-2016).]