You stated in your letter that you just consulted with a Realtor. If you did not sign a listing agreement, you may not even need to sign a cancellation.
In either case, the broker will honor your request.
If, on the other hand, you meant that you have signed a Purchase Agreement with a buyer, it sounds like you may have sold your house. If the buyer ask for repairs you can refuse. If the buyer accepts the property without repairs you could be stuck. In this case you need to talk to an attourney as soon as possible.
Dilbeck Realtors, GMAC
Ask the agent and the managing broker to cancel the listing. If it has been on the MLS and actively marketed, your agent may give you a list of potential buyers who have seen the home. Should someone on this list submit an offer and end up buying the house, the agent will want to get paid. If your home never hit the market and no one saw the house, your agent should release you out of the listing contract without any problems. If there are problems, you should seek the assistance of a real estate attorney.