To dream that you are having a rummage sale signifies that the time has come for you to get rid of the negative things. You no longer need to think about something you do not like anymore, because life is short and if there is something that doesnt satisfy you, move one. If you are buying something at rummage sale, it shows your tendency to help the others.
Dream dictionary: Rummage dream meanings
Your lack of scruples in your attitude will be harmful.