Fine differences one's not seen in pests (7)
I believe the answer is:
nuances
'fine differences' is the definition.
'nuances' can be an answer for 'differences' (I have seen 'Subtle differences ' mean 'nuances' so perhaps 'differences' could also mean 'nuances'). I'm not certain of the 'fine' bit.
'one's not seen in pests' is the wordplay.
I cannot really see how this works, but
'one' could be 'an' (I've seen this in other clues) and 'an' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for nuances that I've seen before include "Subtle differences" , "Suspicion of" , "suggestions" , "Subtleties" , "Fine shades (of meaning)" .)