One offering fake praise, before being collared by dull trustee (9)
I believe the answer is:
flatterer
'one offering fake praise' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'before being collared by dull trustee' is the wordplay.
'before' becomes 'ere' (poetic term for 'before').
'being collared by' is an insertion indicator (I've seen this in other clues).
'dull' becomes 'flat' (similar in meaning).
'trustee' becomes 'tr' (abbreviation).
'flat'+'tr'='flattr'
'ere' placed within 'flattr' is 'FLATTERER'.
Can you help me to learn more?
(Other definitions for flatterer that I've seen before include "Sycophant" , "One uses butter" , "Person who imitates, perhaps" .)