I'd recommend an rac inspection or similar.
I've worked in the motor trade for years and most places will tell you anything just to sell you a car. This is due to most salesmen being paid on commission.
Ask about the warranty, is it their own warranty or a proper warranty company?
Their own warrantys are usually worthless.
I can recommend a company called warrantys 2000.
They also prefer you to take finance rather than pay cash as they make more money that way, if you can afford it pay cash, if you want finance make sure they don't stitch you into a high finance contract as that is also what most garages try to do.
Another thing is check the mileage yourself online, just because a car has service History
it doesn't mean to say the mileage is correct.
You do this by asking them for the reference number from the vehicles V5 and the registration number.
You then use those details on the VOSA website and check the old Mot History
which will confirm all failures, passes, advisories and mileage.