The most common and most likely answer to this crossword clue is the 9 letter word HOMEOPATH
I've seen this crossword clue in The Guardian
H
O
M
E
O
P
A
T
H
More clues leading to the result HOMEOPATH
- Alternative therapist in love course
- Alternative healer's residence on old road
- Medical specialist in operation at hospital
- Quack from duck below nest on way
- In no way a quack, some might say
- Alternative practitioner‘s institution with old approach
- Therapist‘s in work, at hospital
- One offers alternative treatment in way that includes love
- Doctor in love gets direction
Buddy explains!

The straight part
We know that "Quack" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case quack = homeopath.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 HOMEOPATH mean?
HOMEOPATH noun- A person who practices homeopathy.