When a salesperson approaches someone in the visited building that salesman is asking the other person to represent them. In effect to trust them, make a complimentary judgement and then refer them higher up. Your network of people has increased. The referrer has opened the door to you. All this work so why would you want to have it slammed behind you?
That same salesman wants, and needs, to make a good impression in order to better the commission chance - correct?
Here is the crunch. Often people approach someone , they refer them on, consequently the referrer gts trampled on if the sales person attitude rubs the boss the wrong way, or simply offers a good product at the wrong time.
As the sales person disappears out the door the referrer does not even get a good bye or a thank you.
Thirty seconds spend in acknowldegement when leaving gains you miles and minutes when you finally pitch your wears to the boss.