I'm puzzled by that question sometimes. As an REO agent, I hear it from other agents frequently. Most of my listing agreements do not even give me the right to disclose that information until an asset manager specifically tells me to do so (usually via a call for Highest and Best offers). I'll set that important fact aside right now for the sake of discussion.
If I say "Yes," does that mean you are not even going to show the property about which you have, obviously, received an inquiry or which you have spotted for a client? Or would a "Yes" from me dissuade you from writing an offer for a client to whom you have shown the property? In both cases, then, it does not serve my client's best interest to answer "Yes."
Sometimes, a "Yes" from me would serve my client's best interest; and that would be when the other agent would be encouraged to put a rush on showing the house and/or apply pressure to a recalcitrant client who needs that extra push of competition in order to finally write the offer.
Truthfully, though, that is not the case in most instances. When I engage the other agent in conversation about why s/he needs to know if I have offers, s/he usually admits to still being in the stage of deciding whether or not to show the property. The mere existence of an offer eliminates my listing. Given that fact, how would YOU answer the question if you were the listing agent? It might be a bad offer that I have, after all. Your client might be a better match for this property, but we will never know if you don't show it.
What I usually answer, when asked "Do you have any offers" is simply that the property is still available. If an offer has been accepted, I say that one has been accepted (if I am allowed to do so). When I will not elaborate, it is because I cannot do so, either in recognition of my client's best interest or due to my specific contractual obligations.
Don't be surprised, then, if your do-yo-have-any-offers-yet is followed by my, "Why are you asking that question?" It's not me being snarky; it's me trying to serve my client's best interest. Or, maybe I'm just keeping statistics about why agents and buyers ask the question.
Show the house or write the offer, if you really have a client for whom the house is a good fit. Do it right away, just in case I do have offers. You probably asked the question, because you believe the house is a good deal.
By the way, when the property is under contract, the listing says "Pending" or "Pending Continue to Show." Even then, the game may not be over, as contracts fall through all the time.