Mate of mine got one, it was a hard top 5 door and it failed the MoT. Under the plastic bumpers, side skirts and wheel arch extensions, the metal body had rotten through. It looked like the plastic would not allow it to escape so it just rusted through. The sills when as well and there was nothing to weld new ones to. He decided to get another so he could use it as a donor but everyone he looked at was exactly the same.
It appears that good ones are hard to find, but when people do have a good one, they don't want to sell it! Just make sure you get underneath with a torch and screw driver and be aware of any new underseal. Pay particular attention to sills, wheel arches, cross members behind plastic bumpers, and the area where the 'A' post meets the front wing, probably underneath the inner wing and bonnet. Check carpet for dampness and stains and don't be afraid of prodding around with your screw driver. If it's a solid car, there will be nothing to fear, but it's best to find out before handing over your dosh.