St. Mungo’s Hospital for Magical Maladies and Injuries has reported a sharp increase in wand-related burns over the past month, all of which appear to have been caused by wands sold by a wizard calling himself “Honest Willy Wagstaff”...
-- a warning from The Department of Magical Equipment Control about a trader in Diagon Alley (DP1)
There have always been street peddlers on Diagon Alley, and shoppers have always had reason to be wary of them (such as when “Honest Willy Wagstaff” managed to sell substandard wands and loose-bottomed cauldrons a few years back (DP1). However, once Voldemort returned, wizards looking to capitalize on the public fear managed to sell even sketchier items, from Metamorph-medals that simply made the purchaser turn orange or sprout tentacles (HBP5).
Mundungus Fletcher tried to set up a cart in Diagon Alley in 1997 to sell items he’d stolen from number twelve, Grimmauld Place. However, he didn’t have much luck in doing so, as one of his first prospective customers was Dolores Umbridge, who got him in trouble for not possessing a license and then stole Slytherin’s locket from him as compensation (DH11).