Massive shop baffling most agree (9)
I believe the answer is:
megastore
'massive shop' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'baffling most agree' is the wordplay.
'baffling' is an anagram indicator.
'most'+'agree'='mostagree'
'mostagree' with letters rearranged gives 'MEGASTORE'.
Can you help me to learn more?
(Other definitions for megastore that I've seen before include "giant in business" , "Very large shop" , "large outlet" , "Massive outlet" .)