Japanese people: how do you know when “ちょっと…” actually means “no”?

I’m curious about something I’ve noticed when learning about Japanese communication.
When someone says:
「ちょっと…」
「今回はちょっと難しいです」
「また今度お願いします」
Do Japanese people usually understand these as a polite way of saying “no”?
Or can “ちょっと…” genuinely mean “it’s difficult right now” without necessarily being a rejection?
I’m especially interested in how this changes depending on who you’re talking to — a close friend, coworker, boss, or someone you’ve just met.
For Japanese people here: when you hear “ちょっと…”, what do you usually assume the person really means?