as far as I know, in general teh mount of a jewel is an indication of quality. E.g. a gold ring with a stone in it is an indication that the stone is gold worth. Nobody would mount a diamond in a silver or metal ring and vice versa.
As far concerns ebay you are right. The best place to sell things remains the traditional ones. As I´m - as the most of us I suppose - enthusiastic of bitcoin I did this attempt. From my experience I have to say that probably bitcoin are still not used as alternative to money but they are still an investment like gold or stocks.
I have a friend owning web site selling organic food. I convinced him to accept bitcoin. Let's see if there is a reaction of the market in this other area.
Jewel are consumer good, they are not considered an investment, for that you have to buy gold bullions. The difference with other consumer goods such as a phone is that a phone has no value after two years, a jewel preserves his value in the long period. Of course a phone and a cammeo are two different things, there are people that prefer one to the other and other people that have both... 
