When you buy a crystal or mineral specimen for a collection, are you looking for that classic textbook description? You bet you are! But, you often find that there are about 15 others also looking for the same thing.
Do not get discouraged. You bid, you loose, but keep trying, because one day, your personal limit on what you are willing to spend will get you that piece. Do not, however, settle for an inferior piece at an amount that you could have gotten a text book crystal for. If you don't get it today, rest assured, another good one will be put up for auction or in a ebay store.
If you are buying gemstone material, its really hard to gage the quality by just the picture, but, without the picture, its impossible for you to decide. And buying on just the say of the seller, without a picture is just plain absurd unless you are a long time buyer of a seller's material and trust that seller's word.
So, you do need to know the qualities that make that type of gemstone truely a gemstone. Turquoise, for example, is found in blues and greens, depending on many factors. Knowing which grade of color is worth while is your task in order to end up with a real gemstone. Things that help are where was it mined, are there pictures of a finished piece of the material that the seller has made. A country as the location for a mined stone tells you nothing. There are hundreds of claims in which to find turquoise in just one state here in the U.S., do you think they are all of the same quality? Not in any shape or form are they! Even the same mine could have many grades, and only one of those might be gem quality. Learn about your rough before you bid.
There are many dealers on ebay with many nice products. Shop around and compare and get the best stone(s) you can. Buying on impulse, as an example, turquoise, will get you a stone that will fade out quickly in sunlight, crumble or undercut when you touch it to a wheel, or not take a polish worth a darn.
The good dealers will answer your questions, give them time though, some have hundreds of auction running at the same time as well as a regular store to run. They'll answer when they can, but you have to ask the question first.