Say no to commercial product after end of Christmas month (7)
I believe the answer is:
decline
'say no' is the definition.
(I've seen this before)
'christmas month' is the wordplay.
'christmas' becomes 'dec' (Dec is short for December, the Christmas period).
'month' becomes 'line' (I can't justify this - if you can you should believe this answer much more).
'dec'+'line'='DECLINE'
'to commercial product after end of' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for decline that I've seen before include "Evelyn Waugh novel" , "Refuse - to go down" , "Turn down; deteriorate" , "Start to fail" , "increasing weakness" .)