I guess there's certain basic things like size of accommodation and exercise area - fox-proofness of the accommodation/exercise area, cleanliness etc, condition of any existing occupants, who is the main carer (e.g. is this a child's pet and is going to get discarded or locked away once the child gets bored), knowledge (or willingness to listen and learn), that sort of thing.
To a certain extent as well you can play it by ear, like the one I went to on Saturday had 12 rabbits and looking around I could see plenty of straw in their hutches but not much hay, so I asked where they keep their hay. They pointed to a tiny bag on top of the hutches - for that many rabbits I would have expected to see a bale. I guess at that point, if you were to explain to them the importance of hay, you can gauge from their reaction whether they are prepared to listen and learn or not.