Gemstone rough is sold all over the web these days and always the question of quality is first and foremost in most buyers minds.
First thing to understand is that top quality rough will never reach the web unless it is super common. Top notch material is almost always set back for favorite and top dollar paying buyers of long standing. This is true for diamonds to turquoise and were you to be able to sit in on a selling or buying session, you'd understand why. There is and most likely, will always be a market to the super rich, and if your shopping ebay, it's a good bet your not super rich.
So what does that leave the regular lapiday? Plenty, but you have to shop and compare. You wouldn't walk into a rock shop and reach into a bin of dirty rough and bag whatever you pulled out without looking. So, why should you not compare online?
Poor pictures (or a lack of pictures altogether) and high shipping costs are a clue to move on. Some dealers, unfortunately, live in contries in which they have no control over high shipping. The orient is an example. You will pay $15-$20 just to get a couple of carats from there by some courier. The post office may be a poor choice there for any kind of reasonable delivery times, and some dealers just use couriers outright. But this is a facter you need to figure in since the difference in shipping might mean you could get the same locally for about the same price.
Good, sharp, clear pictures are your best guide to buying rough online. Next you want to check the description for size, weight, and the seller's estimate of quality.
When I sell facet grade material. It has to have clear cutting areas, not cloudy or translucent. It also shouldn't be crazed or loaded with veils.
Ratings also are an indication. AA, AAA are sometimes seen. But for what category rough are they? Is it facet or cab grade. Is it specimen quality or collector quality? All these terms will be found in some listings and they can be very misleading if the picture is poor or there are few pictures.
I use a scanner to show my rough and most times, it catches the condition and I can give an idea of size of the rough fairly well. But for opal, it's hard to show plays of color. That's an advantage cameras have over a scanner. But still, a clear picture is worth a thousand words and is what I go on when buying rough.
Diamonds are an interesting and difficult item to buy online. Anyone can use terms used by the major grading labs and some even provide certificates from these labs. But let's face it, if it's price so far below wholesale for it's grade, it most likely isn't close to that grade at all and you'll be upset with your purchase.
Turquoise is another interesting stone. My favorite story is how people strive to obtain material of the quality Tiffany's set 100 years ago. Himalayan Turquoise was famous for it's color and stability. And! it was mined in Southern California! But that's where Tiffany's got it from, and the mine owner also mined tourmaline and that mine is still active and now owned by Pala Industries. At the turn of the last century, it was owned by the Himalayan Mining Company, hense the name.  But, because of it's name, people figured it was from the moutains of the same name and today there is much Persian turqoise on the market. You won't ever find Tiffany grade turquoise on ebay. There is one big market out there for it why would someone waste time selling it in this fashion anyway. But, you will see dyed and oiled turquoise passed off for much better grades. You can't tell if it's oiled unless you can see it in person. That's all there is too it. You can taste the oil or set a piece in blotter paper and tell fairly quickly it's been oiled. Dyed stones are harder, but usually, you can tell right off when you cut a piece in two. The dye stops quite often, just a short distance from the surface. And there are substitutes as well you have to watch for.
When shopping for gemstones, it's best to learn all you can about that stone before you buy. Where it's found and mined. What market prices are currently. What qualities are easily bought. And most of all, what are it's characteristics and what can you expect.

By shopping this way, you'll get material you can have fun with and maybe even make a buck or two.