Diamonds hidden by female in barrels — they're for buyers (4,5)

'they're for buyers' is the definition.
(where people buy things)

'diamonds hidden by female in barrels' is the wordplay.
I cannot quite understand how this works, but
'diamonds' could be 'd' (abbreviation in bridge say) and 'd' is found in the answer.
'female' could be 'she' ('she' refers to a woman) and 'she' is found within the leftover letters.
'barrels' could be 'casks' ('cask' can be a synonym of 'barrel') and 'casks' is present in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).