The panels on a t25 have seams between them. If this link works you can enlarge the image. There are three main panels all with seams between them. The back panel has a seam you can see going across it. The middle panel has a seam about 5cm from the bottom. These seams tend to rust. The first t25 you were looking at had very few of these seams visable this means that they have been filled in. The rust will appear quickly as a good job would still have the seams.
hello, we've had a vwt25 for a fair few years now and can't fault it. Of course it's getting on a bit now[33 years] and various things need replacing/repairing etc, but we've had some great weekends away and meeting same brilliant people at the vw shows. Have a look at the Club 80 90 website-loads of info and some great people who will help you out and guide you through the pitfalls of buying an old t25.Van for sale section as well. I'm a member of it and it's a lifesaver for getting parts/help etc.