I took this to mean "tact and diplomacy."

For example,
... it is possible to say "No" in a nice way.
... it is possible to disagree without being disagreeable.
(By contrast, it is possible to give a backhanded compliment.)

Off of the top of my head, a specific book title doesn't come to mind however there is a plethora of information on web, including on the Skills You Need website.

Somewhat related: the negotiation books Getting Past No and Getting To Yes.