When buying or selling Whitefriars Glass, have a look first at the collectors of Whitefriars Glass specialist site. There are catalogues and photos of all patterns and colours produced. There is also a section on Mistaken Identities, and on the links page details of a new Blog devoted to wrong attributions with great photos of the most commonly mistaken glass., and comparisons with the originals.
There are many other glass makers who produced items that look similar to Whitefriars, but are not, and a bit of research prior to buying or selling will make the experience more enjoyable with some better knowledge.
A Google search will lead you to the specialist site easily with more info on the links page regarding mistaken identities and lookalikes.