Is that listing in contract already?
In today's hot market, many listings go in contract very quickly. Remember, it's more than just professional courtesy to accurately portray the property's status in the MLS, it is your obligation under the REALTOR Code of Ethics. Standard of Practice 3-6 clearly states that REALTORS shall disclose the existence of accepted offers, including those with unresolved contingencies, to any broker seeking cooperation.
So when agents call to arrange a showing, whether showing appointments are set through your office or through a service, make certain they are informed if the property is already under contract. They may wish to show it anyway, and in the seller's best interests it may lead to a back-up offer; but remember, it's your obligation under the Code to disclose!