Where do people put their trademarks for sale?

Trademark is the Intellectual Property which is like any other asset which can be freely transferred. Through Trademark Assignment one can change the ownership of the Trademark by entering into the Agreement in which one can sell it with goodwill or without goodwill.

There are some websites where they provide the platform for those who want buy the registered trademark and for those who want to sell the brand names. Through that platform buyers and sellers can meet and contact each other and can execute the deal. To name one, there is US Trademark Exchange (private organisation).