In most states, a broker has a legal obligation to inform a seller about each and every offer that comes in on a listing—unless a seller declines their right to such communication, opting to be informed only of offers that total a certain percentage of the asking price. Still, a competitive bid can sometimes fall through the cracks, especially if it would require a listing agent to co-broker the deal. It's always in a salesperson's best interest to put forward an offer from an unrepresented buyer before one who is working with a buyer's broker. The second agent, after all, is in a position to split the commission.
"A broker could be fined or lose their license for such an abuse, but it's not so easy to discover the misdeed," says a seasoned anonymous real estate lawyer.