The most common and most likely answer to this crossword clue is the 9 letter word INSINCERE
I've seen this crossword clue in Financial Times
I
N
S
I
N
C
E
R
E
More clues leading to the result INSINCERE
- Popular nieces upset about Republican leader lying?
- Hypocritical trendy church about to admit offence
- Lying, perhaps, in wrong church with religious class
- It’s popular because the Queen’s inside — that’s not true!
- Captains in ceremonial guards guilty of hypocrisy
- Anger, apprehending name as false
- Elected because half were fake
- Certain since recording that some of it is fake
- One sinner reformed, embracing church? Not true
- Untruthful couples used to live here before nursing college
Buddy explains!

The straight part
We know that "fake" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fake = insincere.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 INSINCERE mean?
INSINCERE adjective- Not genuinely meaning what has been expressed; not sincere; artificial.