Any aircraft you're considering buying, look the registration up on G-INFO...
GINFO Database Search | Aircraft Register | Operations and Safety
That will give you the full and correct designation, real hours, and what engine it should have fitted.
There are others, but the most often mentioned source of second hand light and microlight aeroplane adverts is AFORS...
Planes and Aircraft For Sale - Light Aircraft, Autogyros, Helicopters ... (UK)
And before buying an aeroplane, hire a suitably qualified AND INDEPENDENT inspector (LAA or BMAA depending upon aeroplane) to give you a full and frank report on the aeroplane.
Also check with any owners club whether there's any gossip about the particular airframe (and search the registration on the AAIB website to see if it's been crashed, although with a "rag and tube" aeroplane like the Rans or X'Air, that's no big concern as all the bent bits should have just been replaced with new parts).
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