There's a lot of junk out there. It's not always easy to distinguish fakes, forgeries, and imitations from the real thing. One thing you can do, for some objects anyway, is determine what it's made of. As you can imagine, an object made of ivory is worth a great deal more than one made of plastic. Close-up of burning shell.
Objects made of tortoise shell are very scarce, and understandably quite valuable.
Using tweezers, hold the piece over a match. If the resulting smoke smells like burning hair, you've got the real tortoise shell. If it smells like burning plastic, you don't. Perhaps you have an old tie or scarf that you've always assumed is silk. If it smells like hair, it's authentic.