Updating Showing Instructions on MLS
It’s not required by MLS.
And the property isn’t in multiples — at least not until Buyer #2 shows up.
But, in my experience, it’s smart to update the showing instructions for a listing to advise Buyers’ agents that an offer is being negotiated.
I see two advantages, in fact: 1) it can help to flush out another offer, before the Seller commits to the first; and 2) it’s actually a courtesy to Buyers, who can’t complain afterwards that they missed out.
In-Bounds — and Out
What is verboten? (fined, actually).
Letting Buyers (and Buyers’ agents) show a home without letting them know it’s already under contract (technically, called “sold, subject to inspection” on MLS).
Assuming it’s not simply inadvertent, a listing agent (or two) has been known to do that to generate backup interest for the home, or, if the Buyers aren’t represented, to troll for new business.
I believe that latter practice is called “bait and switch.”