How to detect an online scam?

About a month ago i posted a "Summer tutoring" ad on my local town's website. I got one answer back from a guy who is on business in Europe, but lives on the outskirts of my town. Friends of my think that he is scamming me. He has never ever asked me for money. He is willing to send me a money order or bank draft worth $240 for me to tutor his children 4 afternoons a week. How can I tell if he is legit or not?