Place selling booze maintains constant service (6)
I believe the answer is:
office
'service' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for office that I've seen before include "Box ---, ticket agency" , "professional business?" , "Professional or clerical duties are performed here" , "Subsidiary" , "Place for administration business" .)