Many people think sales is a one way communication.
For those, the purpose of the sales is to sell something you have.
That is wrong.

The purpose of sales is to understand and possibly provide the things your customer wants.It may not be the product you sell, but the product you know. So int order to be a good sales, you need to know your customers and you need to know the products which wil includes the products rom other companies.

If you know a good sales people, it is like you have a good consultant at your side.