Assuming that your agent and his/her broker agrees that you may cancel the listing contract, and assuming that there is no "cooling off" period noted in the listing contract, you could relist with another agent or sell the home on your own immediately.
However, there's some pretty big hurdles left. Canceling a listing contract, in most states, is not an easy thing to do. Most Realtor Associations write listing contracts used by Realtors, and work hard to insert wording within the agreement that makes the contract difficult to break. As a result, neither the agent or broker is obligated to cancel the listing or delist your home. So here is what I would suggest...
1. Adjust the Sales Price of the Home - To be frank, so long as the agent is properly marketing your home, the main reason that a home does not sell is price. While changing Realtors might make you feel more comfortable, if the same home is marketed at the same price, it will still remain unsold. So, consider a change to the appearance of the home, spruce up the exterior, add paint to the interior--these won't add value to the home, per se, but will make it sell faster.
2. Talk to the Broker - Obviously, you still want to sell your home, so perhaps its time to talk with the broker about your concerns. The broker is the agent's employer, so bring your concerns to the broker regarding the work of your Realtor. You and the broker can discuss the marketing plan to see a "fresh pair of eyes" might have suggestions that will provide more exposure for your home.
3. Ask for a New Realtor Within the Same Realty Office - Again, this will require talking with the broker, but sometimes the problem can be resolved by asking for a different agent. In some cases, the broker might even suggest an agent that would be more responsive to your needs or may have more experience in selling homes in your geographic area.
4. Ask to De-List the Home for a While - Sometimes, as a listing gets older and older, the home is "overlooked" by potential buyers. Taking the home off the market for 30 days can reinvigorate the listing. During the 30 days, take some time to spruce up the home to make it more presentable to home buyers.
If all else fails, then I would certainly ask to cancel the contract. If you, the agent and the broker have exhausted all means of selling your home, then there is reason on the part of all parties to cancel the contract. Until then, however, try to resolve your problems with any or all of the above suggestions.
Happy New Year, Nancy! Is your property in LF or in Arizona? Is either property your primary residence? I'd be happy to share some ideas with you. (If you already have a real estate agent, this is not a solicitation.) Also you might check out the site http://ree.com/ And talk with your tax advisor for any potential impact there.... more