Why should we hire you?
Do some research on the product/service the company you are applying for deals with, take note on how your background and skills meet the company selling needs and how you could contribute to the company.
Remember that examples of specific situations are always good to mention.
What features, skills or characteristics would you say are the most important for sales?
You can make a list of these required skills before going to the interview and talk about it. Some are: active listening, flexibility, tolerance to frustration, communication skills, customer service skills, etc.
Did you ever have to deal with an angry or difficult customer?
Most of us had to deal with this at some point, so give an example, but remember that the interviewer is asking this not because he/she is interested in the difficult customer but because he/she would like to know how you dealt with the situation so show the interviewer how you kept control of the situation and made the best out of it.
What Are Your Goals?
Again, make a list of all your job-related goals before going to the interview; you do not want to improvise such an important answer.
Have you ever had to change your whole customer approach because the one you were using did not work?
What the interviewer is really asking is: "Are you adaptable when things don´t work one way?" Give a specific example in which approach didn´t work out as expected and then talk about the steps you too in order to adapt yourself and the out coming result.
Tell me of a time you tried really hard but in the end the customer was not pleased, how did you manage it?
For a sales position resistance and tolerance are very basic requirements. Show your interviewer you do not lack such requirements by giving him/her the right example and how easy it is for you to handle those difficult situations without getting disappointed.
Do you usually meet your quotas? How? How do you feel when you don´t?
Look confident when asked this question, the interviewer is looking for your reaction.
What products did you use to sell?
This is a precise question and requires a precise answer. The interviewer wants to know what your background and technical experience is all about.
Do you find sales interesting? Why?
Do not generalize when giving and answer, on the opposite, give very specific and clear examples of the things you find interesting when it comes to sales.
What are "Sales" to you?
Give a picture of how you see the whole sales structure and procedure from the beginning to the closing.