3 years warranty is standard, but make sure everything is there and works. I don't think there have been any recalls - butyou can easily check with a main dealer and get this done.
With a car 2 years old and mileage that low, I'd want to check out the car hasn't stood for a long time. Who's owned it and how have they driven it ? How did the dealer get it ? If the dealer doesn't give a believable story, walk away. HPI check is a must - I wouldn't trust the dealer to do it either.
You recognise the mpg issue, but what sort of driving are you going to do ?- if you do lots of short trips round town the mpg will be <25. My 1.6 diesel struggles to do 30 round town. A few long trips should get a lot better - mid 30's maybe ?
Don't rush to put a deposit down if you're not sure. I got caught buying a C-Maxby putting a deposit down on one and then seeing a much better car elsewhere. The dealer for the first car not only kept my deposit of £500 but pursued me for damages of nearly £1000 on top. Work on the basis that the dealer is a sheister con-man and you'll be fine.