DID YOUR POST NOT APPEAR?

Check the "View my posts button top left of the board.  This list will show all your posts of the last 30 days with a status.  If it was "Not Allowed", there will be a reason.

WAS YOUR AD "NOT ALLOWED"?

Check the ad posting guidelines here to get details after you see what the reason was based on the above.

DID YOUR POST DISAPPEAR?

Check to see what the "Not Allowed" reason is, then think if it was part of a thread that may have gone away.  If the Moderator pulls a post, then all replies to that post get pulled as well.  the replies also get labeled with the same "Not Allowed" reason as the post that was pulled, so you may get a strange reason.  Check with the mod if you are unsure if it was your post, or the post you replied to.

OTHER NOT SO WELL KNOWN RULES:

Never use two handles in the same thread.
No negative comments on a lady's ad thread.  
No "extra" punctuation in subject lines - this is not Craig's List.
No writing in ALL CAPS. It's "shouting" and considered rude.

RULES FOR PHOTO THREADS:
1.  Only 1 thread per day.
2.  Only 1 photo per provider per thread.
3.  No links or advertising of any kind in photo posts.