The most common and most likely answer to this crossword clue is the 7 letter word PATRONS
I've seen this crossword clue in The Daily Telegraph
P
A
T
R
O
N
S
Buddy explains!

The straight part
We know that "Customers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case customers = patrons.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PATRONS mean?
PATRONS noun- One who protects or supports; a defender or advocate.
- An influential, wealthy person who supported an artist, craftsman, a scholar or a noble.
- A customer, as of a certain store or restaurant.
- (Roman law) A protector of a dependent, especially a master who had freed a slave but still retained some paternal rights.
- One who has gift and disposition of a benefice.
- A padrone.
- A property owner, a landlord, a master. (Compare patroon.)
- To be a patron of; to patronize; to favour.
- To treat as a patron.