The most common and most likely answer to this crossword clue is the 17 letter word ALLÂ OVERÂ THEÂ SHOP
A
L
L
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O
V
E
R
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T
H
E
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S
H
O
P
Buddy explains!
The straight part
We know that "Messy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case messy = all over the shop.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.