Policies you have to follow depends on the company you are doing remarketing with.
You need to follow the Personalized advertising policy set by Google if you wish to use Google’s remarketing tools. Read more here: https://support.google.com/adwordspolicy/answer/143465
You need to follow the Custom Audience terms if you wish to use Facebook Pixel. Read more here: https://www.facebook.com/business/help/464299260268383