Insincere person appears to copy their mistake (9)
I believe the answer is:
hypocrite
'insincere person' is the definition.
(I've seen this before)
'to copy their mistake' is the wordplay.
'mistake' indicates anagramming the letters.
'copy'+'their'='copytheir'
'copytheir' anagrammed gives 'HYPOCRITE'.
'appears' acts as a link.
(Other definitions for hypocrite that I've seen before include "fraud" , "Insincere person affecting virtue" , "For example, Tartuffe" , "One who does not practise what they preach" , "Dissembler" .)