Mark of a poor reviewer, they say (9)
I believe the answer is:
diacritic
'mark' is the definition.
(diacritic is a kind of mark)
'a poor reviewer they say' is the wordplay.
I cannot quite understand how this works, but
'a' is found in the answer.
'reviewer' could be 'critic' (I've seen this before) and 'critic' is found within the answer.
The remaining letters 'di' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for diacritic that I've seen before include "grave perhaps" , "Mark" , "one showing a pronounced difference" , "[ACCENT] , perhaps" , "Capable of distinguishing" .)