The most common and most likely answer to this crossword clue is the 10 letter word DEFAULTERS
I've seen this crossword clue in Independent
D
E
F
A
U
L
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E
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S
Buddy explains!

The straight part
We know that "they won’t pay the fees" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they won’t pay the fees = defaulters.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 DEFAULTERS mean?
DEFAULTERS noun- One who fails to fulfill an obligation or perform a task, especially a legal or financial one.