You've prepaid, but an emergency has left your contractor unable to complete or even start the job. The worst part? Your contract says nothing about a start or end date, so you're forced to wait until it's convenient for him to finish up. (Hint: He'll probably prioritize the jobs he hasn't received payment for yet.)
Even if you didn't prepay, some contractors will set up payment schedules that force you to pay in installments before the work is completed. So, you may find yourself paying for 75 percent of a job that's just 50 percent complete. Because you have a contract, he's going to finish the work, but it'll be on his time, not yours.