Julie,
has anybody mentioned that you tend to argue with yourself? What you think is rude and unethical may not be seen that way by others who do not have your background, both business and personal. And the fact that folks are using your business' Facebook page to promote their own "businesses" proves that:
a. they simply don't get it
b. they simply think it's OK
or
c. they've been told that it's OK.

So, obviously, the rules DO need to be posted and understood and folks have to agree to them.

Now, if you were coming to FL and wanted to shoot ring candids I would expect you to email me so I could join you. If I announce on my Facebook page that I'm available for ring candids, it is because I've already discussed it with the Show Chairs/Vendor Chairs and we've come to an agreement. Sometimes that means I have to pay a reduced vendor fee. I'm probably the only one taking candids that has approached it this way. And I don't shoot on spec. I only shoot clients. I don't assume to have rights I don't have and I know you don't either. And as difficult as it is to get consensus on the etiquette of that, it is doubly difficult in a medium that has very little history behind it and, generally-speaking, no rules. Rude is very much within the accepted genre of Facebook, Twitter, etc.

This is not rocket science but the folks involved are not rocket scientists. This is the digital age. Whatever I can do is OK simply because I can do it. I understand and respect your frustration. And I think there will have to be some education involved so folks can, in fact, learn what is and is not appropriate. Oh, and I can tell you that you smell because I'm an honest and candid person . That's how some very rude people see themselves.

Jim