Where some marketers go wrong is by promoting items that have minimal relation or no relation to a group’s objective. For instance, it doesn’t make sense to post flight deals in a group about app development. Similarly, I see many publishers spam Facebook groups with affiliate links, which is a low-probability way to generate commissions. In highly active groups, posts and affiliate links are buried within minutes by newer posts.
Retain some control. If you upload photos of yourself, or friends/family with consent, it's worth going for the 'rights managed' licence option – otherwise you'll have little to no control over how your images are used (eg, you could star in an ad for haemorrhoid cream). See Alamy's page on understanding stock image licensing for more on the different types of licences.
We’ve all heard those horror stories about folks who accidentally published personal content to their employers’ social media channels -- a marketer’s worst nightmare. So to avoid publishing mishaps like those, assign Facebook Business Page roles only to the employees who absolutely need it for the work they do each day. And before you do that, be sure to provide adequate training to those who are new to social media management, so they aren't confused about when they should be hitting "publish," what they should be posting, if something should be scheduled first, and who they should be posting it as.