One of the duties of a listing agent, in my opinion, is to get feedback from agents who show my listings. Most sellers want to know what people are saying about their home and often, until they learn otherwise, sellers start calling their agents for feedback, almost as soon as the buyers have left their home.
Feedback is a funny thing. If a buyer really likes a property, the listing agent won't really need to call the showing agent. The showing agent will call the listing agent to let them know there is interest. If a showing agent doesn't respond to emails or phone calls regarding the showing of a particular property, it's safe to assume there's no interest. Here's the dilemma though. Without knowing WHY there is no interest, a seller and the listing agent can't improve the home and their chances of a sale with the next showing. If no one takes the time to respond to emails and phone calls, and no feedback is given, some things that perhaps the seller could do to improve their home will go undone.
It takes me literally 2 seconds to respond to feedback emails. I try to do it the day or the day after a showing. Yes, I'm busy too, but my sellers like feedback, so I have to assume my fellow real estate agents have sellers that like feedback as well. For me, it's a courtesy that I am happy to do for people that share my profession. Occasionally I get so busy that I may forget, but when the second email comes in, I answer it. It's a common and a professional courtesy.
I've heard all the reasons not to give feedback. You won't tell me one in the comments that I haven't heard already. Feedback is part of our jobs as listing agents, whether we like it or not.