The most common and most likely answer to this crossword clue is the 9 plus 3 letter word ONCE-OVER (-)
I've seen this crossword clue in The Guardian
O
N
C
E
-
O
V
E
R
(
-
)
Buddy explains!
The straight part
We know that "Casual assessment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case casual assessment = once-over (-).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 ONCE-OVER (-) mean?
ONCE-OVER (-) noun- A quick, cursory survey or inspection