Amazon has set up a number of forums for customers to discuss their products, or whatever they feel like talking about. Last year they made a rule. Indie authors may only discuss their own books in the Meet Our Authors forum. Before this authors could try and sell their books anywhere, and some people were annoyed at the sales pitches, which were sometimes irrelevant to the subject being discussed.
Since Amazon does not charge for publishing books in kindle format, a great many people have done so. At first glance it may appear a huge volume of authors are all trying to sell books to each other. This may not be what people envision when invited to promote their book in a forum where people come to chat with authors they like, but it is not as bad as it seems. All good writers, and many mediocre writers, also enjoy reading. While it may be a challenge to get someone intent on selling their own book to buy yours instead, it has been done.
Better yet, there are some non writing readers who visit the MOA forum in search of free and inexpensive books. Every so often someone starts a thread wondering if the forum is limited to authors, and if they ask nicely, some lurking readers often uncloak themselves.
Some have asked for the forum to be divided up by genre. This does not seem likely to happen in the near future. Amazon's current attitude is that sales posts outside MOA should be deleted, but that MOA itself is a wild frontier, and no attempt can or should be made to police where people post inside it.
Even the frontier has written and unwritten rules. You cannot post working hyperlinks in MOA, the software is constructed so they do not function unless you cut and paste. There is a designated linking technology for linking to your book from the discussion boards, no pictures or outsized text links are permitted.