Seller initially taken in by customer, a joker (7)
I believe the answer is:
punster
'a joker' is the definition.
(I've seen this before)
'seller initially taken in by customer' is the wordplay.
'seller initially' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'taken in by' indicates putting letters inside.
'customer' becomes 'punter' (I've seen this before).
's' going into 'punter' is 'PUNSTER'.
Can you help me to learn more?
(Other definitions for punster that I've seen before include "Comedian" , "One who plays on words" , "user of wordplay" , "One makes jokes" , "Verbal joker" .)