The most common and most likely answer to this crossword clue is the 12 letter word OVERESTIMATE
I've seen this crossword clue in The Guardian
O
V
E
R
E
S
T
I
M
A
T
E
More clues leading to the result OVERESTIMATE
Buddy explains!
The straight part
We know that "appraisal’s too high" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case appraisal’s too high = overestimate.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 OVERESTIMATE mean?
OVERESTIMATE noun- An estimate that is too high.
- To judge or calculate too highly.