Periodically, there is a great gnashing of teeth over frauds, fakes, counterfeits, and other bad stamp-related things, and nothing ever comes of it. I suspect this is because humans are human. They would like to own a rare stamp or two and even suspecting that the stamp or stamps they are buying might not be genuine, they still want to own it. In fact, if they are explicitly told the stamp they want is not genuine, that it's only a "copy" or a "reproduction" of a rare or uncommon stamp, they'll still buy it. I've done that. Mea culpa. There are many blank spots in my albums for stamps I'll never own. They're too rare and too expensive even if I could find a copy to buy. A few times I've mounted a similar-looking stamp in that space, knowing that anyone with any common sense will realize it's not the real stamp. In fact, maybe it's even a copy issued by
that country's postal service. It's not unusual for a country to issue stamps in honor of earlier stamps. The U.S. honored its first two stamps from 1847 with a souvenir sheet it issued a century later depicting pretty accurate images of those same stamps. What if I buy one of those souvenir sheets (they're cheap) and cut out the two stamp images and mount them in my collection in those two blank spaces? Did I just commit a crime? Hardly. Any collector who would think they were the real things would be a real amateur. Many countries do this. I recall the Netherlands and Sweden and many others have honored their early stamps by issuing government-printed reproductions. And the U.S. has done this more than once. It reissued the entire Columbian series, among others, albeit with minor changes. A collector with only mnodest resources could take those reissued, much cheaper, Columbians and mount them in the spaces for the real ones, and the result would look pretty good. Nothing wrong with that. They're "copies," but no one is trying to cheat anyone -- and that last part is the important thing. The first part, that there are copies for sale, is pretty minor stuff. just don't lie about what they are.
If you buy, as I have a few times, stamps advertised as copies or reproductions because they are the only way I'll ever own that stamp, the only way that space will ever be filled, who have I harmed? Especially if the stamp has "faux" or "copy" or "reproduction" on the back. I even make it more obvious to anyone who inherits my collection: I write "copy" below the stamp in my album. I don't want anyone thinking it's a rare stamp even if it's a pretty decent reproduction of a rare stamp. And it's also marked on the back of the stamps. If copies or reproductions are not marked as such, then there might be a problem, but usually there isn't any problem. Have you even looked at the awful quality of most fakes? They are so obviously not the real stamps, it's laughable. What is not quite as laughable are photocopied fakes of real stamps that look just like the originals and are claimed to be the originals. Those I'm a bit scared of since they could fool a lot of even good collectors. But mark them as "copies" and you're just fine in my book.
On the whole, I just smile at the regular appearance if frustrated anger at fakes and reproductions. They've been around since stamp collecting has been around. You aren't going to stop them. And, no,
eBay and any seller is not responsible for employing a squad of stamp experts to examine the authenticity of every stamp offered for sale. That's up to the buyer, hence the phrase
caveat emptor. Ask for a certificate or get one soon after buying if you're spending a lot of money. Otherwise, write "copy" on the back of the stamp, and enjoy filling that empty space even if it's not the real thing. I own a few paintings that look remarkably like the work of famous artists but it doesn't reduce my pleasure in owning them. When they get sold later, even though they're well done, no one is going to be fooled.
I'd guess that 80% of the early stamps of Japan for sale
at any time anywhere are fakes. It was just the practice back then to make copies of stamps to sell to collectors. As the demand for Japanese stamps rose way beyond the availability of early stamps which had apparently been issued in very small numbers, up stepped some pragmatic individuals who produced some very good (sometimes) copies of those stamps. Entire books have been written to distinguish the various fakes and forgeries from real stamps. You could make an entire collection just of these stamps, and some collectors have done that. I don't see it as a moral issue to get worked up over. It's capitalism at its finest. Find a market and satisfy it as best you can.
Meanwhile, I have more blank spaces to fill with something that looks at least a little like real stamps. As long as I'm not told fakes are "real" or "genuine" and charged accordingly, I haven't been cheated.