Whilst one should always be aware that there could be fakes and forgeries, I think it worth pointing out that there are very few known fakes from the last 150 years for British glass. That doesn't make it impossible just that it is more likely to find something that has been doctored/improved to make it more valuable.
For instance, some years ago a dealer in Portobello Market used to have blank glasses (and occasionally decanters) embellished with little star cuts as they found them very easy to sell at that time. It is not unknown for collectors to add labels, or signatures, to items to 'improve' them and make them more valuable/desirable.
No-one can be sure this hasn't happened to them (that is, been sold something) at some point in collecting, or dealing, but naturally with time comes experience and the knowledge of what to look for. Joining the GMB also helps a lot

Hmmm, now for the 'advert'....... If you are new to collecting it is always advisable to find a dealer who has a good reputation and buy from them. They will not only be a barrier to anything mentioned above, but you have the protection, that if found to be wrong, the dealer will give you your money back and take the loss themselves. They will also give you advice while you still buy from them.
Happy collecting out there

Cheers, Nigel