I've just been to look at it again. I can't see any rust apart from a bit of surface rust on the inside of the drivers door. It looks too good to be true but they say it hasn't had a respray. It's done 80 000 miles so that's better than i thought. Underneath is rust free and so's the exhaust. Maybe it's in the minority and stayed rust free?
Auto trader give some good tips on what to look for when viewing a second hand car. They advise what to look for on different makes and models and they were spot on when I was looking for a Ka soft top. I walked in in my heels looking like a dolly bird and the guys thought they saw me coming... Until I got down on my hands and knees and starting looking under the car, pulling back the carpets, asking why the number plates had been changed from the original etc. It was quite funny watching their faces change while I blagged I knew what I was talking about. One guy offered me a job haha. I found a few with problems, one had been in a crash (number plate gave it away and I got under and had a look and bumper had massive crack running along the back... Think they parked it up against the window for that reason) and one was a ringer. Others had problems that auto trader had warned about. Managed to get myself a decent one in the end. You can sometimes tell if a car has had a respray by looking under the rubber seals by the windscreen. If it's a cheapo respray job that theyve done just to sell, they probably haven't taken the rubber off.