Policies you have to follow depends on the company you are doing remarketing with.
Google:
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
Facebook:
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