You speak to someone at an event, you chat to someone on a plane, you meet someone at great Aunt lena's 86th birthday.you chat for 5 minutes and 32 seconds and they hand you their business card and say, "If ever you're looking for an expert on XXX do give me a call."
Would you ever? I wouldn't. Building trust takes time, you have to be patient. a very dangerous activity is recommending one person to another when you aren't sure of both of them.
BUT when you are it is a win/win/win situation.The person you refer is a winner, the person you have introduced him to is and you definately are.