The compare prices on Bidz are absurd, but there are great bargains to be had. Do not
let yourself fall in love with an item on Bidz! Most items will be relisted many times, as they deal in quantity.
If I may offer a suggestion, here are some tips for valuing potential purchases from Bidz:
Get the gold price in grams from Link hidden: Login to view
Multiply this per gram price by the fineness of the gold. 24k gold is 100% pure gold; 18k is 75%, 14k is 58.5% etc. So at the current spot price of $31.35/gram, 14k gold has a spot value of ($31.35*0.585) $18.33 per gram. Most Bidz listings specifically state the weight of the ring, so multiply this weight by the spot price -- an average 6 gram ring at 14k fineness has $109.98 worth of gold in it. If you can get your bid anywhere near this price you are doing very well (every so often -- rarely -- I have purchased a ring with stones for less than the spot price at Bidz. It's a great source.)
Regarding stones, stay away from lab created and stick purely to natural ones. Gem values are highly subjective, and there are many varieties, so I won't get into specific valuations on each, but bear in mind that for the most part Bidz is not selling super high quality stuff -- their precious stones (diamonds, rubies, sapphires ad emeralds) tend to be very low quality unless they are accents, so avoid them altogether unless very specific quality info is given and a very clear picture is given.
Hope this helps!