First, advice I once gave someone at one of those Oriental Rug auctions held in hotel ballrooms:
"Be prepared that what you buy will be worth half of what you pay for it."  The listener was ready to hear me say "worth  twice what you pay for it" and had to ask me 3 times what I had actually said/meant. 

The same goes for the Native American jewelry sold on ebay and elsewhere, in shops, on web sites and almost anywhere else you can find it. What's the statistic? Gallup supplies 90% of the market in the US, and 75% of what flows thru Gallup is Pacrim. That is, imported from Pacific Rim countries.  Something like that. Multiply those two numbers together and you get about 65% of the jewelry represented as Native American in the US, when sold as new or up to about 20-25 years old, is imported.  Those statistics are about 8 years old. The proportions are probably higher now. 

We're not even going to attempt to discuss the idea that turquoise-looking stones aren't really turquoise;  they're powder/plastic/lucite or similar. Or that mis-marking of silver is rampant. Or that coral is not. Or that chip inlay is tinted macaroni.

Caveat emptor: Don't buy anything unless you know what you're doing, or don't care.  You are very unlikely to find a hidden treasure here.  I was among a few early complainers who were instrumental in getting ebay to require sellers to state country of origin on their Native American jewelry listings. Country of Origin? Not the US. Isn't that perverse?

True story:  long ago, I actually found a treasure here on ebay, a rather unique Zuni flat inlay squash, vetted by the best. And you know what? Not 3 weeks later, a copy of it was listed,  by a  seller whose business is apparently trolling ebay and then subcontracting folks in the Pacrim to produce copies. This happened more than once. He is among those required by ebay to state that his product comes from abroad. Sadly, several sellers whose inventory is partly imported are not required to so state. Ebay seems to have policies which are unevenly imposed regarding this.

 Be especially skeptical of ebayers who say that the best way to find a real piece of Native American jewelry here is thru the seller's FEEDBACK!  That is just completely false.  You have 100,000 buyers who know nothing, and  give positive feedback to sellers who sell fakes, and there is no way out of this vicious circle. Except education. You become knowlegeable by looking at hundreds of pieces, in person, in your hand, assuming some of them are good. (This is a huge assumption.)

Anyway, the rant is over.  Be careful out there. Be careful in here.