I used to work together with a sales guy and he both increased revenue and made customers happy, mostly by chatting with people about their issues on the phone

I used to work together with a sales guy and he both increased revenue and made customers happy, mostly by chatting with people about their issues on the phone and inviting existing customers out for dinner to solicit feedback and/or tutor people on how to better use our software. Him showing prospective customers how to make our software work for them produced both healthy revenue boosts for us, and also large monetary savings for our customers. Similarly, introducing the right IBM technology into your company can be a purely positive game-changer. While there are certainly dishonest sales people out there - just like there are dishonest programmers -, it wouldn't be fair to derogate all of them as "leeches".