If you dream of the yard sale, it means that you are trying to get rid of things in your life or emotions that cause you negative feelings. The yard sale that is made by other people shows that you are trying to get the advice from others.
Dream dictionary: Yard sale dream meanings
In the dream you are at a yard sale, this shows you ability to learn from the past and to use your experience in order to avoid misfortune. You want to learn to use your long ago forgotten talents and skills. Now you have an ability to learn from your own mistakes.