Thanks for your input Pete, I decided it wasn't worth the £11.25 return postage that it was maintained I must pay, or the small partial refund, so I told the seller to forget it and left honest feedback, as the seller seems to sell a fair amount of glass and I felt people should be aware. The whole attitude was rather sarcastic and unfriendly so I went with what I felt was the right thing.
I think the seller knows the truth of the matter, but didn't want to be liable for return postage which he probably would have been had he admitted inaccurate description. It could have been easily settled as I never wanted to return it anyway, it's more of a research piece for me rather than for display, a simple reduction due to the damage and I would have been quite happy, but the attitude made it impossible.