Diminish qualification somewhat diminished after receiving commercial endorsement? (7)
I believe the answer is:
degrade
'diminish' is the definition.
(thesaurus)
'qualification somewhat diminished after receiving commercial endorsement?' is the wordplay.
'qualification' becomes 'degree' (university qualification).
'somewhat diminished' means to remove the last letter.
'after receiving' is an insertion indicator.
'commercial endorsement?' becomes 'ad' (short for advert).
'degree' with its last letter taken away is 'degre'.
'degre' placed around 'ad' is 'DEGRADE'.
(Other definitions for degrade that I've seen before include "Deprive of dignity" , "Cheapen, bring disgrace on" , "Lower the quality of (something)" , "Break down, deteriorate" , "Shame" .)