A buying signal may come as any of a variety of types of often subtle cues that the mood has shifted, and the other person is now ready to agree . . . or at least to be open to what you propose.
I came on a recent article on the website of Britain's New Scientist magazine that's very relevant to our main topic here, which of course is Selling face to face. The article: "Come-to-work eyes: Secrets of interview success," by Michael Bond. After all, walking in to meet with a sales prospect isn't so very different from walking in to a job interview.
The link is below so you can read the whole article, but here are a couple of things that particularly struck me.
Read "Come-to-work eyes: Secrets of interview success" at New Scientist website