If a prosect ever comes out to meet you and says that he is "too busy to see you today"
, believe him! Don't try to force a quick sales pitch in the lobby. Give him/her your card, schedule an appointment. "I understand, I apologize for dropping in unannounced, when would be a good time for me to come back?" is usually a pretty good way to handle that.
Tip: Just as important as leaving a good first impression is not forcing a situation that will leave a bad first impression.