and therein lies the problem

You can attribute your glass, in writing, to whatever takes your fancy (and there's a lot of fancying going on out there) - but it needs only one person to be able to show beyond doubt that this attribution is false, and immediately those words become misleading and a subsequent sale based on the original description probably fraudulent.
The problem lies in evasive descriptions which may not refer specifically to a date, a maker or style - such words as rare and old are subjective and probably nigh on impossible to disprove - and probably not worth the time anyway.
Plus the old bugbear of knowing that it's not always possible to be certain of facts by looking at a screen image only.
I just don't think it's worth the time and effort of bothering to go down that road, and to some extent it is a case of caveat emptor, especially if you're considering spending big bucks on something you know know nothing about - you should take the time to gen up on what you are buying. Dodgy sellers are a problem in all walks of life.