I can't tell if a girl is simply dodging hangout plans because she's busy, or if she's using it as an excuse to not go out with me.

Is there a way I can be direct with her, without creeping her out to get to the bottom of it? Or what big hints/red flags go up to indicate that she's not interested in the same manner I am? Should you go all out to find out and have full closure? Or is it a better idea to not know for sure, but still have some sorta dignity/self-respect.

TL;DR - What's your cue that the bitch girl ain't interested?