Among the dealers i know very few vendors who deceive intentionally, but generally they have far less accurate knowledge than specialist collectors and optimistically want to make a good sale.
Generally i buy in the flesh, not online or mail order, -from antique market dealers who are not very interested in their small bits if they arent gold or gemstones, so i dont even see stuff thats very highly priced. Under such conditions every purchase is an exciting risk, and occasionally there may be a treasure among the oddments.
there are ways of sharing what we know about beads without antagonising the person who is offering them. -perhaps by introducing the element of adventure and discovery together, and some copies are as interesting as what they imitate, reflecting another aspect of craft skill...