Hiya. I've bought a few things from GEMS TV and always been very happy. They say the starting prices are not an indication of worth or value, but 'just a place to start'. If you are a sad case like me and watch a lot you'll get to be able to predict the final price fairly accurately from the 'start price' and the number of items in the game to begin with. I have never bought any high value stuff like tanzanite or diamonds, and so I've never had any valuations done, but I'm sure from looking at similar items of blue topaz and citrine etc on the high street and online that I have got good value and definitely not been ripped off. So I would say give it a try, maybe start with something relatively inexpensive and see what you think.
SM