Worrying about whether or not if a girl is gonna flake is like worrying about if the sun is going to rise.
If it's going to happen, it's going to happen. And if it isn't, then it isn't. The only thing we can do as men is ask the girl out. If the chick isn't interested, and she flakes out, then that's on her. You can't avoid it, because as we all know, sometimes a girl just isn't interested.
You just have to go into this game knowing that you can't bat 1.000. The only way to truly avoid flaking is to avoid asking women on dates. And there's no way we're gonna stop doing that.
So, warning signs or no warning signs, if the night ends with a girl flaking, then it's on to the next one.