To buy a car from a dealership or off hands

[Timide]

What is your experience? My DH laughed at me when I said I want to buy our first car in the UK from a dealership (with a warranty, a right to return, fully serviced, the MOT done, etc). He said they will rip money off me and I will end up with a wreck. I see he has a picture of a Warmwood type of place in his head.
But I also have no experience. Maybe it is true I'm not from the UK to know better. What is your preference?
How do you check a second hand car advertised on Facebook? Can you even test drive it? (I don't have any insurance atm). Will the seller be willing to take it to a garage for a check? Seems unlikely, no? So is it a cat in a bag?

I have always used dealerships and never had a problem, I'd only buy direct from a friend as I don't know enough about cars. The AA used to do a service where they'd check a car for you, which might be a sensible compromise. You will definitely pay more through a dealer, but most are decent and will give you peace of mind.