Realtor,
I would never leave a client without knowing their reaction to the house you've just showed them. I wouldn't frame it as a problem, but I'd ask questions like:
How does this home compare with others you've seen? How well do you think this home would fit your needs/family/lifestyle, etc. Can you see your family being comfortable in this neighborhood? And the list goes on, there are tons of questions you can ask to get a feel for their reaction. And, they can be asked in conversation, not like an interrogation.
Besides that, you probably want to help them find the home they'll end up buying. I'd find out what their needs are, find other listings to show them, stay in touch. You need to position yourself as their real estate advisor, not someone who just shows them the house listed by your broker that they called about. Jump in and make them clients, not just people you showed an office listing to.
Hope that makes sense.
Kathleen