Is it farther or further?
1670s, slang, perhaps a schoolboy shortening of Latin flagellare "flagellate." Related: Flogged; flogging.
To offer for sale; peddle, esp in the sense of public hawking: I went to the convention to flog a new book/ Motel and bus companies flog special charter rates
[British 1919+ fr armed forces; fr British slang flog the clock, ''move the clockhands forward in order to deceive,'' applied later to the illicit selling of military stores]