Overact badly, receiving worried member's standard warning (6,6)
I believe the answer is:
caveat emptor
'standard warning' is the definition.
(legal term)
'overact badly receiving worried member's' is the wordplay.
'badly' indicates an anagram.
'receiving' means one lot of letters goes inside another.
'worried' becomes 'ate' (I've seen this before).
'member' becomes 'mp'.
'overact' with letters rearranged gives 'cavetor'.
'ate'+'mp'='atemp'
'cavetor' enclosing 'atemp' is 'CAVEAT EMPTOR'.
(Other definitions for caveat emptor that I've seen before include "at your own risk" , "Warning to buyers" , "Commercial advice" , "purchasing principle" , "Let the buyer beware (Latin)" .)