"Free frog-skin belt with every purchase"
-- advertisement for Madam Malkin's Robes for All Occasions (DP1)
Madam Malkin’s Robes for all Occasions Summer Sale on Now! is a clothing advertisement appearing in the Daily Prophet (DP1).
An advertisement for Madam Malkin’s shop appears on the front page of the Prophet, offering several types of robes (including slimming and lengthening), and including a free offer to entice customers to come for the sale (DP1).
The idea that you could purchase beautifying or slimming apparel is also advertised in the Muggle world, but one hopes that the Wizarding versions live up to their advertising.
Although the date printed on the first Daily Prophet Newsletter (DP1) is 31 July 1998, the timeframe for this event is 1992-1993.
From the Web
Writing by J K Rowling on Pottermore:
Harry Potter Wiki: Madam Malkin's Robes for All Occasions