A glass case nearby held a withered hand on a cushion, a blood-stained pack of cards, and a staring glass eye. Evil-looking masks stared down from the walls, an assortment of human bones lay upon the counter, and rusty, spiked instruments hung from the ceiling. Even worse, the dark, narrow street Harry could see through the dusty shop window was definitely not Diagon Alley. (The Sorcerer's Stone, 49)It is during that first accidental trip to Knockturn Alley that Harry sees Draco Malfoy and his father come into the shop, Borgin and Burkes. Harry notices Malfoy reading the note on an opal necklace about how it is cursed and has killed 19 muggles, which we know later he attempts to send to Dumbledore, accidentally cursing Katie Bell instead.
The place has a bad reputation, as is evidenced by the Weasley's refusing to let their children visit it, and by Hagird chiding Harry, "Skulkin' around Knockturn Alley, I dunno - dodgy place, Harry - don' want no one ter see yeh down there -" (The Sorcerer's Stone, 54).
Harry's next visit to the alley though is purposeful. He, Ron, and Hermione see Malfoy looking suspicious and follow him, "For Malfoy had glanced around, then slid into Knocturn Alley and out of sight" (The Half-Blood Prince, 123).
It surprises me that Borgin the shop owner is so easily flustered by Malfoy's threats, "Harry saw Borgin lick his lips nervously" (The Half-Blood Prince, 125). I would think working in a shop like that would draw all sorts of unsavory clients. It probably wasn't the first threat he'd heard, and probably not the last either.
Borgin knows full well where his is located, what he sells, and what kind of customers those products attract.
As for me, I don't think I could visit Knockturn Alley, because though the Weasley boys expressed disappointment in not getting to experience it, I would be afraid and uncomfortable.
On Monday, the fabled lost diadem of Rowena Ravenclaw will be the focus of my Harry Potter themed A-Z post.