How to Stop People from Posting Spam on Your Facebook Business Page
Fourth step: On the upper left-hand corner of this page you should see "Timeline" and "Tagging."
(Please see the image below to see what it should look like).
Click on Timeline and Tagging. Now, find the setting "Who can post on my timeline?" Next, click "Edit" which will be on your far right.
Now select "Only Me," from the dropdown menu.