To today's costume jewelry dealers and collectors, this is a very important question. In the interest of educating vintage jewelry collectors and dealers alike, I have accumulated a bit of information on the fakes that are out there, and am presenting this knowledge here, so that everyone can make better-informed decisions about vintage jewelry purchases. I will be adding to this collection as time goes on. It may save you a ton of moola.
Provenance can be hard to prove.
Read, study, and learn all you can. Also, some dealers are knowingly selling fakes . . . Be tight-fisted with your money, and don't buy unless you feel comfortable and have done your homework. Be wary of familiar-looking pieces that sport another designer's name. For example, neither Boucher nor Hobe made jelly bellies . . . period.