Auction ales off (4)
I believe the answer is:
sale
'auction' is the definition.
(type of sale)
'ales off' is the wordplay.
'off' indicates an anagram.
'ales' is an anagram of 'SALE'.
(Other definitions for sale that I've seen before include "Period of low prices" , "Occasion for buying at reduced prices" , "Disposal - auction" , "See 12 Down" , "Retail event - town in Greater Manchester" .)