Are you seriously asking how you can possibly avoid raping someone? And you want to be taken seriously?
If you can't tell if they're openly and honestly consenting, why are you pushing them to have sex with you? That's already a problem.
Because he's not ensuring that she's freely consenting. If you can't be sure, you shouldn't be pushing them for sex.And if he just asks someone if they want to have sex with him, and that's the whole conversation, and they say yes without expressing any emotions of fear, how is that his problem?
How is this hard to understand? Stop hunting for the plausible deniability where you can get away with raping someone. Christ.