Do you want a necklace or other piece of pearl jewelry, or do you want loose pearls to make your own jewelry?
The price usually tells you the quality as far as roundness goes. The priciest pearls are the roundest and smoothest and most lustrous. The next most pricey are less round and or smooth, but just as lustrous. Even commercial or beading quality pearls can be intensely lustrous. They just won't be very round. It is easy to see good luster. The more shiny, the better. The more orient, the better, and these can be found in pearls of almost any price level.