I usually buy the well used and heavily used items from Wex,
MPB etc.
Never had a problem from the UK suppliers and the prices reflect the condition and your warranty is the same.
I had a terrible lens delivered by adorama to my us address, it was a NIkon 24mm that was wrecked to be honest, full refund so no problem.
My gear takes a beating as it is so I don't worry about the well used / heavily used items. I bought a used body from wex under a condition 8 I think and it was fine, I wouldn't hesitate on their lower grades - as long as you know it'll looked used!
I bought a Nikon 300mm F4 from
MPB and most of the paint has rubbed off! Scratches to the front element etc. but it works great! and was super cheap. I called them to inform them that the lens cap was incorrect (it was shipping with a 77mm as opposed to 82mm) and they refunded £25! Not bad on a lens that was priced at £160