Diamonds are the only gem stones that have standards of quality so you want to pay close attention to these standards when you are buying diamonds. As for as other gems go, it is up to you and the jeweler to decide their value. The are quite a few gems that are being synthesized now and you should learn which ones are and how to recognize them. Rubies for instance will have a “tagant” in them that is visible when the synthesized stone is held under ultraviolet light. There are many types of stones that look similar, so be aware of what they are. For instance yellow quarts and citrine are often mistaken for yellow topaz and rhodolite and grossular garnets are much rarer then red garnets but they can look the same to the untrained eye. If the deal looks to good to be true then it most likely is, so never jump at a hasty deal the requires that you pay quickly or sight unseen. Also, remember that the type of lighting can and will effect the color of a gemstone. The best way to see a gemstone is in normal out door lighting. Of course, no jeweler is going to let you walk out the door with a fine piece of jewelry, so they should have decent lighting for you to examine the gemstone with.