All I can suggest is that you get the cars reg checked as it only cost a few quid.
I have had a few occasions where people appear to be private sellers and have actually been traders. When you call tell them you are calling about the car they have for sale. If they say which car then they are probably traders.
It might seem trivial, but if they are going to deceive about being a trader, what else may they be hiding?
The price does seem a little on the high side for a car with cat d against its name.
If you do go for it, I would try and get a few quid of the price advertised.
Best of luck.
"O Romeo, Romeo! wherefore art thou Romeo?