Dodgy cult with unique feature for those buying into it (7)
I believe the answer is:
suspect
'dodgy' is the definition.
(I've seen this before)
'cult with unique feature for those buying into it' is the wordplay.
'cult with' becomes 'sect' (I can't justify this - if you can you should believe this answer much more).
'unique feature for those buying' becomes 'usp' (abbreviation for unique selling point).
'into it' means one lot of letters goes inside another.
'sect' enclosing 'usp' is 'SUSPECT'.
(Other definitions for suspect that I've seen before include "Imagine guilt" , "Dubious" , "Dodgy" , "One is believed to be guilty but without proof" , "Doubt - man being questioned by police" .)