The Better Business Bureau actually sent out an alert about this, saying that scammers could be knocking on your door asking if you need a service done, or there could be bad companies out there who won't follow through after you hire them.
The best thing you can do is research a company before you hire them; make sure you are researching them on Google and with the Better Business Bureau.
Also it's always a good idea to get two or three different estimates, if you have time. Compare those before you buy.