My understanding is that Kerso imports the lenses correctly, and due to the fact they have an international warranty there is no issue whatsoever.
I believe that the cameras Kerso gets are also imported properly, however, they state they only have warranty in the US on their registration card. However, I believe that there has never been a problem with a camera getting warranty that Kerso has imported. I believe you get a full UK receipt.
This is something that you might be lacking getting it from ebay.
I would think it is relatively safe using Kerso