No one likes being sold or told. Ask first saying please and then thank you. If that doesn't work and then you may have to tell them. If that doesn't work and perhaps you are their manager, you may have to give a direct order. Hopefully it doesn't get to that point. In order to learn and grow it goes back to the old sales saying, you have two ears and one mouth so you can listen twice as much as you talk. It's the right thing to do to model the way for others and improve communication.