Sells fantasy film, cutting dirty bits (7)
I believe the answer is:
markets
'sells' is the definition.
(I've seen this in another clue)
'fantasy film cutting dirty bits' is the wordplay.
'fantasy film' becomes 'ET' (ET the Extra-Terrestrial).
'cutting' means one lot of letters goes inside another (some letters cut their way into a word).
'dirty bits' becomes 'marks' (dirty marks).
'et' inserted within 'marks' is 'MARKETS'.
(Other definitions for markets that I've seen before include "Trading places" , "Commercial activities where goods and services are bought and sold" , "Places for buying and selling" .)