I wager this could be an unpleasant flatterer (6)
I believe the answer is:
earwig
'an unpleasant flatterer' is the definition.
'earwig' can be an answer for 'flatterer' (I've seen this before). I am unsure of the 'an unpleasant' bit.
'i wager this could be' is the wordplay.
'this could be' indicates an anagram.
'i'+'wager'='iwager'
'iwager' anagrammed gives 'EARWIG'.
Can you help me to learn more?
(Other definitions for earwig that I've seen before include "An insect; to eavesdrop (slang)" , "Insect with large rear pincers" , "flatterer" , "Common garden insect" , "Small insect with aural toupee?" .)