Carmarthen Cameras,
MPB, ebay.
On ebay gbr.13 is the best seller I have dealt with.
Ebay is fine, you are well protected, but you need to know what questions to ask, honest sellers are willing to give answers fully and quickly
And don't get caught by delaying tactics, if something is not right, fill in a return immediately and include photos with the return application.
If a seller accepts the return immediately or automatically, they are not penalised unless you decide to leave non-positive feedback.
If an item is listed as "used" that means it works, no matter what the seller may put in the description.
Shpock is a big no, full of rip-off dreamers; gumtree and FB only if you can collect
One way for ebay if you want to buy anything, post the users name here and see if any one has had problems with them.