The game’s up: sell! (4)
I believe the answer is:
'sell' is the definition.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for flog that I've seen before include "Hit - sell" , "Keep hitting" , "Beat with a whip or rod" , "Beat with whip or slangily sell" , "Scourge, whip" .)