Mr. Borgin owns a shop in Knockturn Alley (a Dark magic street just off Diagon Alley): Borgin and Burkes. Harry lands there by accident thanks to a mishap with the Floo network. Lucius and Draco Malfoy turn up at the shop while Harry is there, so Harry hides. Harry watches Lucius selling some poisons that he doesn't want the Ministry to find on his property. Mr. Borgin accepts the poisons and treats Lucius with lots of respect and sucking up. As soon as Lucius and Draco leave, though, Mr. Borgin starts muttering, "Good day yourself, Mister Malfoy, and if the stories are true, you haven't sold me half of what's hidden in your manor" (4.98). So all of Mr. Borgin's careful greetings are just for show; really, he seems to loathe Lucius.