How do FB privacy settings work?

[Deathbound]

So there is this person I know and I don't to friend them, they are kind of off and I don't want to give them the ability to post on my wall. When we were friends they would post all sorts of inappropriate crap on my wall. Now this person is entertaining and I don't mind having conversations with them in the comments section of a post, its not as big of a deal if people see that. So if I can see some of what they post does that mean I can see everything they post, and vice versa can they see everything I post, assuming neither of us have changed our privacy settings?

The reason I ask is because they do post interesting stuff time to time and I'd like to see it.

TLDR summary: If I can see some things on a person's wall I am not friends with does that mean I can see everything they post?

[Amanda]

You can see all of their public posts only