Is it permissible for a web hosting promoter to receive a commission, knowing that these hosting services might be used for both permissible and forbidden purposes (such as forbidden advertisements or publishing articles without citing the source)?

The default ruling is that it is permissible for you to promote hosting services and earn money from them, as the determining factor is the purpose for which websites are created. Incidental matters that the website was not created for, such as prohibited advertisements, music, or forbidden images, do not prevent promoting website creation as long as their primary purposes are permissible.