An auction was a method of bartering in which the product was bid for by the audience with the highest bit winning.
In 64, in Rome, Barbara Wright was sold by Sevcheria to Tavius for 10,000 sesterces after a slave auction. (TV: "All Roads Lead to Rome")
Jamie McCrimmon was kidnapped by the Voraxx, who brought him on board their slaver ship and intended to sell him in a slave auction. He was rescued by the Second Doctor and Zoe Heriot. (COMIC: POT 2)
The Dalek nicknamed "Metaltron" had been bought in a private auction by Henry Van Statten for his collection. (TV: Dalek)
In the Unthinkable City, specifically created on 21st century Earth, an auction to sell the Relic (the Doctor's corpse) was set up by Qixotl. (PROSE: Alien Bodies)