A scout in jumble sales (8)
I believe the answer is:
auctions
'sales' is the definition.
(I've seen this before)
'a scout in jumble' is the wordplay.
'jumble' indicates an anagram.
'scout'+'in'='scoutin'
'scoutin' with letters rearranged gives 'uctions'.
'a'+'uctions'='AUCTIONS'
(Other definitions for auctions that I've seen before include "Public sales to the highest bidders" , "Cautions about public sales" .)