Don't talk to strangers?

Today the washing machine repair man came over. To repair the washing machine. Anyway, Olivia smiled at him as he entered, and then we showed him down the basement laundry room and left him to do his thing. Awhile later, he came up to ask a question, and when he headed back downstairs, Olivia started crying. She was suddenly attached to him! When he finished the job and left, she cried again, and we had to stand at the door waving bye-bye to him for five minutes! He probably thought we were crazy. How am I ever going to teach this girl not to talk to strangers?