"....all of which appear to have been caused by wands sold by a wizard calling himself 'Honest Willy Wagstaff'"
-- Department of Magical Equipment Control (DP1)
Honest Willy Wagstaff was a street peddler who was accused by the Ministry of selling defective goods in Diagon Alley (DP1).
Wagstaff has sold defective wands and loose-bottomed cauldrons to unwitting buyers. The wands caused burns to a number of people (DP1)
The English surname Wagstaff is thought to date to the 16th century. It can either refer to a man who would wave (wag) his staff or rod of office to catch the townpeople's attention before delivering news or to a man whose actions should not be mentioned in polite society
When someone labels himself or herself "Honest xxx" there does arise the thought that they may have been suspected of not being quite so honest in the past.
The Department of Magical Equipment Control which warns against Wagstaff does not exist in the Ministry of Magic structure in later books (OP7). It may be a division or office under the Department of Magical Law Enforcement.
While the date printed on DP1 is 31 July 1998, the timeframe for these events is 1992-1993.