In the 2000s, Archer & Lewis were estate agents who sold 36 Bannerman Road twice: the first time in 2008 to Alan and Maria Jackson (TV: Invasion of the Bane), and the second time about a year later (TV: The Last Sontaran).
Fliant Wormbleeder was an intergalactic estate agent. After he lost a handheld device involved with his work, a young boy named Robbie accidentally sold the Earth to three different alien races. When Wormbleeder was contacted by the Tenth Doctor, he managed to find suitable home planets for those species. (COMIC: The Day the Earth Was Sold, The King of Earth)
The Galparians were estate agents who sold legal unclaimed planets. These planets were often inhabited, but lacking official documentation for ownership by their inhabitants. As part of a "beautification" process, to attract buyers, the Galparians released a virus which returned life on the planet, considered "pests", to primordial soup. The Seventh Doctor said he feared them. At some point in the far future, the Galparians attempted to claim the Earth. (AUDIO: Dead to the World)