"I noticed someone I'd rather not have anything to do with on Mary's friend's list. I'll call him Joe. I noticed that if I comment on something Mary said, then Joe comments later, I can see what Joe said, even tho he's not my FB Friend. So I'm concluding Joe can also see what I said?"

Yes, Joe can see what you posted because you posted on Mary's wall. However, if Mary posts on your wall...Joe cannot see what she's posted because he doesn't have access to your Wall.

Carrie's Wall - is Carrie a FB friend with Joe? Does she have her security set to high? If she's not a friend and she has high security, Joe won't be able to see anything on her wall, Mary or not. If Carrie is Joe's FB friend AND/OR she has low security...then you post on her wall....Joe will see your post.

I think I've got these right. It's the owner of the wall that's being posted on and their security that drives what others can and can't see.

I'm not sure re: your question about 'Carrie', but regarding what you post on Mary's wall.... yes, Joe can see your posts if he is friends with Mary. However, there is a way you can make yourself absolutely invisible to Joe, I think you block him somehow. I'm in this situation with my sister. If I do a search for her in FB (and vice versa) it's like she doesn't exist. I know she comments on family posts, etc., because I'll see someone say "thanks Sue", but I can't see what Sue herself said. If that makes sense, lol.

Rilie is correct; block Joe & he's done with seeing anything you post period. I have my son's GF blocked after an incident last year where they broke up; I also have my 2 "sisters" blocked.

Now; keep in mind Joe can make a new FB account & will be able to see everything again.

The way FB is supposed to work is that if you put people into groups; you can control what they see & what they don't on your own page- it gets sticky when you post on other peoples wall depending on their privacy. I can't believe the number of people that allow friends of friends to see everything. I'm pretty sure FB is set like that unless you change it higher.

FB is getting too invasive for me; I've been debating getting rid of it but I enjoy it.

I could be wrong, but I have a bunch of friends that are my friends only because we play games together on FB. The are in a list of friends I made called "gamers".

My default setting for posting is =hide from "gamers"=.
My hope is that they can't read my general posts, since I really don't think they are interested in my life LOL.

I can change the setting each time I post something (there's a little lock right beside the "SHARE" button). Sometimes I want to post only to them, or to include them in something I think is important.

Have to say after reading this I'm glad I never started on FB. My sister loved finding an old classmate, but is realizing what a pain it is avoiding some of the other jerks out there.

iknownothingatall- yes; it's supposed to work like that with groups but doesn't always work for some reason.

Just confirms why I won't touch Facebook.

Shoot, this came out long (ended up venting something else).

Carrie's Wall - is Carrie a FB friend with Joe?
Not yet, but I figure it's just a matter of time (they all know each other). Not sure what Carrie's settings are at. Without coming out & asking, is there a way to find out?

Rilie is correct; block Joe & he's done with seeing anything you post period.
That's posed a problem for me. I have tried and can't find a way to make it work unless he's a Friend. IOW, I got into Account>Privacy Settings>Customize. First option is "Posts by Me". I can edit that to where it's "Friends Only Except..." and then I type in name(s). Friends names will work, but I just tried it, typed in Joe (not my Friend) and it didn't keep that setting, it just disappeared.
If there is another way, I'm all ears! :) Same thing if I want to do a custom edit for maybe one post. It only takes Friends names as exclusions.

Wait, just found something. I was in Account>Privacy Settings and see "Block Lists" at bottom center of page. I experimented entering "John Smith" . (I don't know a John Smith, so no harm done.) It let me block & unblock him, so it's doesn't have to be a Friend or permanent block. However, this is what is blocks: "Once you block someone, that person can no longer be your friend on Facebook or interact with you (except within applications and games you both use)."

I don't use apps or games, so it sounds like even if I put Joe's name on the block list, tho he can't interact with me, he could probably still see my posts left on Mary's wall. Since I'm stepping out of my own territory when on her wall. :/

Natal, I have become a bit disillusioned. There are pitfalls. My now single best friend from H.S. closed her account due to a creeper who wouldn't leave her alone. I treasure my family, but sometimes what younger ones post (teen to early 20's) makes my jaw drop. TMI to an extreme. Don't want to know about the younger (early 20's) distant relative who had an affair with a 'bad boy' type, broke up her marriage, lost custody of her toddler, now in a custody battle. (Common sense would dictate in a custody battle, don't post certain things.) Ironically after all that the bad boy's possessiveness showed even on FB, she broke that off. She lost a lot for a fling. I just don't want to know that stuff (why anyone would think the world would either is beyond me).

Another thing (just a rant). My FB times are very early a.m. before work, or evening 'down' time. Ideal for chatting with family overseas due to time difference. I work at home, nearly all of it on PC. Recently a sibling's spouse & I were chatting, they said winter has been super busy. I agreed, mentioned how many hours I've put in lately too. Their response was condescending and came with a smile similar to one they'd use trying to catch their kid in a lie; "are you suuure...? " *smacks forehead* Of course I'm sure. And I take breaks, who doesn't?! My 'work' days can go 12, 14 hours when I'm on a roll. So I bop online, rest my brain, get a brief change of scenery. Certainly don't need to justify that to them. Didn't pursue it, but was ticked & insulted. Because their response came from them seeing my FB activity. They aren't even on FB, so they are seeing through one of their kids I'm close to & Friends with. That's a little too weird for my liking.

Love the 'real time' staying in touch, but reading above, it sounds crazy. Have some family that refuse to do FB. Think maybe they're the smart ones.

Or what about the family members who "friend" you and you confirm because you feel you "have" to. Then you go back and delete them later on (they don't need to know my biz) and what the heck....they "friend" you again!? Can't win for losing, LOL. FB is great to keep in touch with long-lost friends but a royal pain when it comes to family "spies" wanting to know your biz.

You have the right place to block- he will not see anything you post on anyone's wall. I share friends with my blocked siblings; I can't see their comments nor can they see mine- we can't see each other on friends lists either; the only way I know they are posting a comment is when someone says their name- one of their names are not common- their nick name is not common either; so if I see either; I know they've posted.

If you block; then unblock; you will have to wait 48 hours before you can block them again.

hit submit too quick...

Go to his page & block him from there. On the left side column; under the picture & friends; you will see Report/Block This Person- that's the easiest way to block someone

Thanks roselvr, for the added illustration, I will do that!