Trader in basement reportedly (6)
I believe the answer is:
seller
'trader' is the definition.
(I've seen this before)
'basement reportedly' is the wordplay.
'basement' becomes 'cellar' (basement room).
'reportedly' shows a homophone (sound like).
'cellar' is a homophone of 'SELLER'.
'in' acts as a link.
(Other definitions for seller that I've seen before include "One who disposes of" , "Resell to vendor" , "Trader" , "Person making sale" .)