Gloryhole question

So even tho ive been in several gloryhole situations, i still consider myself a novice and need to ask a question. When the dick pokes thru the hole, i know im going to suck it like a champ, but my question is how will I know if the guy also wants some ass?? I ask the question cause there have been some dicks that i wanted to fuck, but didnt cause I didnt want to kill the mood. Should I just assume everybody wants to fuck when in the gloryhole?? Help me out Xhamster....i want to be an expert gloryhole slut