How/where do/Should men draw the line between a girl "playing hard to get" and her just Not being interested?

When my wife and I were dating in college, she was at a different university and free to date others. She told them about me, but some guys were convinced she was just playing hard to get. She made a point to introduce them to me as "the one that I love." We shook hands and they stopped pushing her and just enjoyed being a friend with benefits.