"Full disclosure" is the name of the game to attain the status of HONEST SELLER in any business. There are those who operate with that goal and those who don't. A smart buyer seeks out those who do. Society/Association memberships, while no 100% guarantee of integrity, go a long way to inentifying those who are willing to operate in an honorable fashion.
Unfortunately, online venues like
ebay are perfect breeding grounds for the ethically-challenged who will try to avoid full disclosure as much as possible. This manifests itself in many ways in listings;
Inaccurate identifications, misleading or incorrect quoted values, inferior pictures, unwillingness to show the backs of stamps, no word descriptions at all - just pictures, unfair or inadequate return terms (such as selling "AS IS" items that are well-known to be faked, such as better flat plate coils, etc.
It behooves all buyers to "be careful out there". The ethically-challanged are all over the place. Support a site like Stamp Smarter whose mission is to try to help rid online venues from problematic material by educating both buyers and sellers. You can help. Please do.