The most common and most likely answer to this crossword clue is the 9 letter word CLOTHIERS
I've seen this crossword clue in Independent
C
L
O
T
H
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R
S
More clues leading to the result CLOTHIERS
Buddy explains!
The straight part
We know that "They sell many a garment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they sell many a garment = clothiers.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 CLOTHIERS mean?
CLOTHIERS noun- A person who makes or sells cloth or clothing.