Practically every Disco I out there will have the rust thru at the rear door/wheel well area. Most will have some degree of rust under the rear mat because it acts like a giant sponge and retains any water that ever gets back there.

Most rust thru in little holes by the Alpine windows and or leak at the seals of the large rear side windows eventually. Drain lines for sunroofs leak.

Also under the carpets in the front floor board. The 95 is over 15 years old man.

To determine if it is surface rust or complete rust thru give it a good hard look. Scrape the surface with a putty knife or better yet a wire brush. Tap on the floor panels with a hammer to see if it bust thru.

You can deal with significant surface rust on panels. Get under it and bang on the frame with the hammer, see if the frame is solid or shot.

Offer him a price you can deal with or forget it.