Is it permissible to include affiliate marketing links in an e-book without informing the buyer, or should a direct link and a marketing link be provided so the customer can choose between them?

It is permissible for the seller to include links within the electronic books and materials they sell, even if these links generate a marketing commission, provided two conditions are met: that the links lead to websites that publish permissible content, and that they are placed in a way that does not harm the buyer. If the buyer is harmed by these links, for example, if they are repetitive or placed in an inappropriate location, then the buyer has the right to return the purchased material.