Right folks, hope you will allow me some leeway here. Been motorcycling the best part of 25 years now, but want to know:

What is the best way to buy a second-hand bike these days?

Have had by current machine since 2009, bought at Main dealers. (no complaints)
Before that Bought Bike from a friend, (still friends with him)
Bought a piece of dog poo of a GTR from B&S (never again),
Bought bike from friend, (right bike at right time)
Bought bike from Larger dealer (no longer trading)
Bought two learner bikes from main dealer including one new vehicle.

Technology has moved on a bit since the days of classified ads in the paper, so what has been the best way to find the bike you want?

Is Dungdeal full of con artists? Will you get a better deal if you buy in the UK? Are you better off staying in the motorcycle shops?

Thanks for all the usual help I know you will give.