The most common and most likely answer to this crossword clue is the 9 letter word EVALUATOR
I've seen this crossword clue in Financial Times
E
V
A
L
U
A
T
O
R
Buddy explains!
The straight part
We know that "One determines the worth of" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one determines the worth of = evaluator.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 EVALUATOR mean?
EVALUATOR noun- Agent noun of evaluate; one who evaluates.