Thanks for the question, silicium.
With some exceptions, we've allowed the occasional buying/selling/trading of manuals, books, and other types of documentation. Copyright law in most countries permits such activity as long as the materials were obtained legally and the copyright holder attached no additional licensing terms to the materials.
Some books, manuals, and other forms of documentation carry licenses which prohibit sale or transfer. Offering to buy/sell/trade such materials is not permitted on Nekochan.
Examples of these kinds of materials include many technical repair guides written for use only by authorized service providers, materials used in commercial training courses, documentation produced explicitly for certain types of government sales, etc.
There haven't been a lot of requests to buy/sell/trade manuals here, and, aside from a small number of cases where someone wanted to sell materials that obviously had licenses that prohibited resale (which we blocked), members have seemed fairly responsible about deciding what to put up for sale. As a result, the occasional buying/selling/trading of manuals, books, etc. has been allowed here on Nekochan.
Please exercise a bit of judgment in deciding what types of books/manuals to offer to buy/sell here. Do not try to offer to buy/sell/trade materials that have licenses that prohibit buying/selling/trading them. If you expect the owner of this site or the moderators to act as lawyers or to communicate with lawyers, then you might expect to see the buying/selling/trading of all manuals to be treated - very quickly - like the buying/selling/trading of commercial software.
I hope that helps to clarify things.