I’ve asked this in another forum but my post quickly moved down past the front page and I don’t think anyone’s going to notice it. Hopefully there are some relevantly knowledgeable Dopers!
I’m wondering what happens exactly when you delete a message from a conversation with an individual in Facebook. I assume they don’t also see it deleted? But do they see that you deleted it?
No, the other person can’t see that you deleted it. It’s like an email. If I delete it, you can’t see that I deleted it.
If you aren’t facebook “friends” and you delete the entire thread, the other person will know the next time they send you a message. It will be preceded by a “do you accept this person’s message” prompt which has to be selected before you can reply. I know this isn’t exactly what the OP was asking, I just thought it might be helpful.
I don’t accept messages from people I’m not friends with, so I don’t know how that works. 
I recently deleted a friends comments and he immediately responded “deleted?!” So, it seems like he could see it and perhaps was notified. Can say for sure though.
That has consistently been my experience. I even tried it with a friend the other day. I wrote her a response in our conversation thread, and she received an announcement that a message from me had arrived. I deleted it before she opened up Messenger, and she says she could read it.
That’s why you haven’t responded!
No, they can see it was deleted if they look at the thread again, but are not notified. I have had a few instances where gay marriage or other LGBT issues come up and a right wing friend from high school can’t wait to chime in that he thinks being gay is wrong, so I delete his comments since he is unaware that I have a number of gay friends, and I don’t agree with his views. Since this only happens once every couple of years, I just politely remind him not to push HIS political agenda on MY wall, and he calms down, but he was definitely pissed off he was being censored when he went back to look at the thread to see if anyone else agreed with him.
We’re mixing walls with messages here.
OP, what was your intention? Is there even a way of deleting one individual message? I can’t see how.
So, are we talking wall postings?
I deleted a message to someone, but a couple of hours later he responded to it, so it was if it deleted it from my version of the thread, but it was still on his. I thought if I deleted it, it disappeared from both, especially since I was the original sender. Guess not.