A true psychic would have ideal flexible work: they could just show up 30 seconds before clients walked in I often think of this when I see "Open" signs on psychic shopfronts, but no apparent custom. Yes, it's a joke, I understand the issues..
Maybe they’re not actually in there, but know nobody will come in until the right moment, so thus completely safe to leave the door open. At the ordained time the psychic simply walks in the back door and sits down.