One who sells revolutionary communist paintings (6)
I believe the answer is:
trader
'one who sells' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'revolutionary communist paintings' is the wordplay.
'revolutionary' says the letters should be written in reverse.
'communist' becomes 'red' (red can informally mean communist).
'paintings' becomes 'art' (painting is a type of artwork).
'red'+'art'='redart'
'redart' back-to-front is 'TRADER'.
Can you help me to learn more?
(Other definitions for trader that I've seen before include "One in business" , "One selling" , "Person in the business of buying and selling" , "Tarred the dealer badly" , "Red tar (anag)" .)