Wine collection merchant picked up (6)
I believe the answer is:
cellar
'wine collection' is the definition.
'merchant picked up' is the wordplay.
'merchant' becomes 'seller' (seller is a kind of merchant).
'picked up' indicates a 'sounds like' (homophone) clue.
'seller' is a homophone of 'CELLAR'.
(Other definitions for cellar that I've seen before include "Container for salt" , "Where provisions may be stored" , "Storage space below ground" , "Underground store room" , "Underground area" .)