You can usually express “No” four times before actually saying the word.

1st No: How am I supposed to do that?

It has to sound like a request for help. Properly delivered, it invites the other side to participate in your dilemma and solve it with a better offer.

2nd No: some version of: Your offer is very generous, I’m sorry, that just doesn’t work for me.

3rd No: I’m sorry but I’m afraid I just can’t do that.

4th No: I’m sorry, no.

–Never split the difference, p.181