To dream of a yard sale represents the recycling of past experiences, ideas, or relationships. Considering using something old, neglected, or uninteresting to others for new purposes.
Negatively, dreaming about a yardsale may reflect jealousy that someone is not considering your feelings about the past. Watching people you know start new relationships with people you don't want to know anymore. Frustration that the past isn't being allowed to settle or be forgotten. Being inconsiderate of others feelings about the past.
Example: A women dreamed of seeing her ex-boyfriend take things out of her parents basement for a yardsale. In waking life she was upset and jealous that her parents wanted to start a new friendship with her ex-boyfriend.