When it’s too soon, as the following question:
"If we were to meet here, right here, exactly three years from today, what must have happened both personally and professionally in your life to be really happy with your progress?"
Memorize this question. It’s probably going to be the most useful question you know.
If you ask this question to the other person, and they give you a long answer, it means they’ll buy from you (or date you or vote for you, etc.)
If they give you a short answer, or they don’t give you an answer at all, they’re not in to you. They don’t want to buy from you or date you.
I know it’s harsh, but wouldn’t you want to know right away than after you give a 2 hour sales presentation or after you’re married and the marriage goes astray?
Seriously, take the time to memorize this question. Then actually ask it.