"If it doesn't seem to work the first time, don't give up or assume the spirit did not show up."
This x100000, and as a matter of fact don't assume that whatever you're speaking with has left, even if you go through your protocol of choice.
If you jump the gun on that part you might find yourself in a very bad long-term kind of situation, and don't even assume you're talking to whatever you think you are, or take anything you learn as a fact, treat everything with the same credibility that you would overhearing a rumor around the workplace from someone you do not know and verify anything of significance or application independently.
I mean I don't want to sound jaded about it, but really.