The seller must tell you about the rule when you purchase the item and give you two copies of a cancellation form. If you don't receive a form send a letter. The seller has 10 days to refund your money and 20 days to either pick up the item or provide shipping costs for you to return it.
There are a few restrictions which you can read here.
Also, most towns require door-to-door salesmen to obtain a permit and adhere to restrictions (these are different for each town so look on your local web site) such as:
- No person shall solicit within the public right-of-way of any street or highway
- Solicitation and handbill distribution is not permitted between the hours of 9:00 p.m. and 9:00 a.m.
- Solicitors and handbill distributors may not solicit or leave handbills at premises when a sign has been posted giving notice that solicitors are not welcome, such as “no solicitors” or words of similar meaning
- If a person uses a vehicle in solicitation activities, there must be a sign located in a conspicuous place on the vehicle, identifying the name of the person or the company that the person represents. If the name is an individual, it must be followed by the word “solicitor”. The lettering on the sign must be at least two and one-half inches high
- Solicitors and handbill distributors must wear a traffic safety vest