I have a masters degree in Negotiation & Conflict Resolution. There's two books that give you negotiation superpowers:

1. Getting to Yes
2. Getting Past No

Those two books by themselves are enough to truly learn how to become an adept principled negotiator.

I'd like to see "Getting to Yes" or "Getting Past No" in addition. I think both of these books are great at helping founders understand that negotiations are not zero-sum games.

Check out the good book "Getting Past No" (the follow-up to "Getting to Yes") - this is called having your BATNA - Best Alternative to Negotiated Agreement and will help your position even if you don't have to bring it up, just having it in your mind could boost your confidence and help you ask for what you want

My go to books for negotiating:

* Getting Past No

* Getting To Yes

I've read both a few of the negotiation books (Getting to yes, Getting past no) and Five Dysfunctions and I don't know that I'd recommend them, to be honest.

My beef with Five Dysfunctions is primarily the book recommending MBTI. MBTI has the predictive value of horoscopes, more or less. Really hard to take anything said seriously at that point.

The negotiation-series has some value, and has helped me succeed in some negotiations, but I'd honestly recommend Never split the difference as a substitute. Having read that book instead would probably have saved me more than a few poor outcomes in negotiations.

Finally I'd like to recommend Peopleware - surely one of - if not the definitively - best book I've read for professional purposes.

Books I liked:

- Bargaining For Advantage (https://www.amazon.com/Bargaining-Advantage-Negotiation-Stra...)

- Negotiation Genius (https://www.amazon.com/Negotiation-Genius-Obstacles-Brillian...)

- Getting To Yes (https://www.amazon.com/Getting-Yes-Negotiating-Agreement-Wit...)

- The Coursera course from the University of Michigan (and not the Yale one).

- Getting Past No (https://www.amazon.com/Getting-Past-Negotiating-Difficult-Si...)

- Difficult Conversations/Crucial Conversations/Nonviolent Communications

The last bullet (arguably the last two bullets) are about conversation skills, but that is an essential part of negotiations.

I won't claim to be good at this stuff. It takes a lot of effort and practice to change habits you've formed your whole life. But still, I've improved somewhat. What I do think I've become much better at is identifying why someone's efforts succeeded (or in this case, failed).

I would also recommend Influence by Cialdini. It is not a negotiation book at all, but will make much of the material in those books more meaningful if you've read this book.

Books/courses I discourage:

- Never Split The Difference

- The Lynda course (there may be more than one now, but the one I took years ago was bad).

William Ury, of "Getting to Yes" fame, also has a book titled "The Power of a Positive No" that directly addresses your question. It should be required reading for all software developers. http://www.williamury.com/books/the-power-of-a-positive-no/

Really, if everyone on Earth read those two books and his "Getting Past No", the world would be a much happier place.