Deal in small beer (4)
I believe the answer is:
sale
'deal' is the definition.
(I've seen this in another clue)
'small beer' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'beer' becomes 'ale' (type of beer).
's'+'ale'='SALE'
'in' is the link.
(Other definitions for sale that I've seen before include "Auction; Cheshire town" , "From which one may get bargains" , "Period of reduced prices" , "Auction - somewhere in Greater Manchester" , "Transaction" .)