Please give the name of the e-book, thanks. FWIW, this happens with regularity in my area. Stranger lady comes to a Milonga. She is a nice looking, nicely dressed, and nicely made-up lady, but 40+ years old. She sits alone, at the edge of the dance floor in plain view of the dancers, and Miradas/Cabeceos steadily the whole time. She does not get asked for half the night, although sometimes some of the other ladies will talk with her. Finally someone breaks the ice and asks her, everyone sees she is actually good (as someone serious enough to do Tango out-of-town tends to be) and then she'll dance steadily the rest of the night. It seems this falls into the "not knowing you" category. On the other hand, a 20-something lady gets ask right away! She also steadily gets dances even if it is her first night of dancing ever. Maybe you should add 3rd and 4th categories: Age and beauty.