"You Can Negotiate Anything" by Herb Cohen. While not a sales book per se (like the title implies, it's about negotiating) it gets you into the "sales" mindset.

"You Can Negotiate Anything" by Herb Cohen. While not a sales book per se (like the title implies, it's about negotiating) it gets you into the "sales" mindset. The sales mindset is about figuring out what matters most to the other party, and how you can provide it to them at minimal cost to yourself. Put like that it sounds very abstract and obvious but the book has a number of amusing anecdotes to illustrate these ideas.