There is sometimes doubts as to whether a girl/boy is DTF or not but there are certain things they can do to show that they are even more than DTF, and that is being DDTF. Someone who is DDTF doesn't play around and is straight to the point that their objective is your dick/pussy and they aren't down for the small talk.
Dude I was in the club last night and I was dancing with this girl. And when we were grinding she asks if I can fuck as good as I dance. From she said that I knew she was DDTF.