Welcome to business. Without a signed contract, you don't have much to go on. Courts tend to favor the homeowner over contractors anyways. What's to say that he couldnt' cancel service at any time. If he was obligated for xx period of time, that should be in writing. And then they still have the option to cancel within 5 days of signing the contract.
Even if you did have a signed contract - ask yourself if you want to work for someone who doesn't want you? Sometimes you just have to let them go regardless.
Lawn Lad, Inc.