How to get the trust from the first meeting? And how to maintain and develop long-term relationship?

You cant get trust personally anymore even if you do all what Thanh says. They are all right that you build it but so many things happens before and after your 1st meeting.
Here are what you must have right so you can think of a smooth and quick building of trustful relation:
Your past jobs on linkedIn what will they say?
What your facebook says?
Who your friends are on FB?
What you rate like on anphabe?
The referral you gave are they reputable on paper? On FB?

Check your "trustability" with a headhunt friend before if you want, they do that every day