Retailer of wine collection, say (6)
I believe the answer is:
seller
'retailer' is the definition.
(thesaurus)
'wine collection say' is the wordplay.
'wine collection' becomes 'cellar'.
'say' indicates a 'sounds like' (homophone) clue.
'cellar' sounds like 'SELLER'.
'of' is the link.
(Other definitions for seller that I've seen before include "Trader" , "Person making sale" , "One who disposes of" , "Resell to vendor" .)