Sales etiquette is crucial: Concentrate on listening instead of selling.
One thing that you are taught in sales is that whomever is asking the questions is in control. Well if you don't listen to the answers, then you will never be able to take control of the sale since you never listened to what the customer told you what that they wanted in the first place. This will lead to repeat questions, thus turning the customer off.
In sales it is too easy to get in the bad habit of just looking for that "next" sale and not really paying attention to what the customer wants. The customer always tells you what they want you just need to listen. Listen for verbal clues and non-verbal clues. The more you listen, the more money you make in sales because people love to buy. They just need to be sold! Remember this! After asking for the sale, "Shut your mouth and Open you ears!"