As I am watching other sea glass sites, I am discovering there are more and more ways of describing fake sea glass and misleading or confusing the customer! Just saw a site selling orange earrings for $12, and the description is that they are inspired by the ocean, cultured sea glass! Well, orange sea glass is one of the rarest colors to find, and to find two matching pieces would be next to impossible, but to sell them for $12 -- obviously they are not genuine sea glass earrings.
Recently, in a store in Florida, the shopowner showed me some "sea glass" earrings. Again, they were perfectly matched, identical turquoise triangles (another rare color). I looked at the card describing them, and it said they were sand tumbled. Clearly, you can toss in some sand in a tumbler, and voila, you can create your own fake sea glass.
Genuine sea glass has been tossed by ocean waves for months, more likely years. People study the origins of the sea glass found on beaches -- old bottles, glassware, boat lights, etc. A well regarded book on the subject is Pure Sea Glass by Richard LaMotte. If you are serious about sea glass, check it out.