I live in the USA. I bought a 1984 Mercedes 307d motorhome in the UK off an internet ad which did not have a picture. I am very happy with the purchase. I think the key is to evaluate the seller as much as you are evaluating the vehicle. I trusted the seller and I thought he was honest. I would be very leary buying from a dealer in similar circumstances. Someone mentioned the problem that the seller, while honest, may not have the ability to give a good mechanical assessment of the vehicle. In my case, the price was vey good, I like taking gambles now and again, and even if it was a complete bust, I was only out $1800.
I did not lack my doubts. Try buying a transatlantic airline ticket and travelling halfway around the world to pick up a vehicle you have never seen. A lot of my friends thought I was nuts. Imagine my relief when the taxi pulled up to the campground and there the vehicle sat in quite good condition. (The owner had already moved to Spain so I never actually met him. The corner newsagent store was holding the keys and registration for me)