Coucil Tax Band.
How long have they lived there.
How old are the fixtures, roofing, windows, doors etc.
How long has it been on the market?
When was the boiler last serviced?
Has there been any re-wiring or internal refurbishment in their time there?
What is the neighbourhood like in terms of crime, personal safety at night, etc?
Have they been victims of any serious crime or anti-social behaviour around the property?
What are the neighbours like?
What's the local transport infrastructure like? Easy to get a bus etc. if necessary?
Local amenities, eg. schools, surgeries, shops etc?
After speaking to them, go round knocking on a few neighbours' doors and ask them their opinion of the area, and the house in question. If you start to get a bad vibe... walk away.
I can't stress enough that if this is a purchase you are considering, bring a dictaphone and record the entirety of your conversation/answers to questions from the current owners. If they say the area is quiet, and they've never had any trouble only for you to move in and discover that the property is the favoured bullseye for the local pond life (as happened to us), you'll need the recorded proof in order to raise a case for Misrepresentation in the courts. Otherwise, it's your word against theirs and nothing will stand up.