Poorly rated commercial activity (5)
I believe the answer is:
trade
'commercial activity' is the definition.
(trade is a kind of commercial activity)
'poorly rated' is the wordplay.
'poorly' is an anagram indicator (a poor spelling).
'rated' with letters rearranged gives 'TRADE'.
(Other definitions for trade that I've seen before include "Business - (kind of) wind" , "Transaction" , "Calling" , "Commerce - traffic" , "Skilled occupation" .)