Stake fish for shop (6)
I believe the answer is:
betray
'for shop' is the definition.
(I've seen this before)
'stake fish' is the wordplay.
'stake' becomes 'bet' (synonyms).
'fish' becomes 'ray' (ray is a kind of fish).
'bet'+'ray'='BETRAY'
(Other definitions for betray that I've seen before include "shop" , "Break confidence" , "Inform on (someone)" , "Inadvertently reveal" , "Cheat on" .)