I agree LL.
I had a contract with a commercial property last season ...after a spring clean up, the customer found out that she had signed on for 2 years with the previous contractor. Here she was with 2 contractors signed up and in distress. I politely told her not to worry about the contract with me. She paid me for the spring clean up.... I did the snow removal for her this winter and now this year, will be doing the mowing etc.
Guess what Im trying to say is ..don't worry about it. Handle it in a courteous manner and chances are they will do business with you again when the "lowballer" screws up.