4.9 Advertising External Websites/Commercial Advertising
The term 'commercial activity' mentioned in the following section includes any action involving monetary transactions, whether it is the user selling or buying a product/service. Exceptions can be made (think of charities), but they're very rare and you should not expect to have one.

The use of Planet Minecraft to obtain free advertising or to promote other websites is strictly forbidden. This includes, but is not limited to, posting referral links to other websites. Posting on the site, forums, or chatroom is for non-commercial purposes only. You may not post in any manner which promotes, or is intended to promote or generate revenue, for a business enterprise, or commercial activity. This includes, but is not limited to, individuals selling items, persuading a user to endorse a page on a social media site in return for reward or gain, or posting through link shortening services such as AdFly. For acceptable use of AdFly, please see the appropriate section below under the Submission Guidelines. Posting advertising content such as this is prohibited in all areas of the site, including forum signatures and your about me section, and ignoring this guideline will result in a ban. Posting advertisements for any site that is intended to perform a service that Planet Minecraft is intended to perform, such as server listing, is not permitted.