Swindle by company? Make sure! (7)
I believe the answer is:
confirm
'make sure' is the definition.
'confirm' can be an answer for 'make' (thesaurus). I'm not certain of the 'sure' bit.
'swindle by company?' is the wordplay.
'swindle' becomes 'con' (con is a kind of swindle).
'by' says to put letters next to each other.
'company?' becomes 'firm' (firm can mean a company or business).
'con'+'firm'='CONFIRM'
Can you help me to learn more?
(Other definitions for confirm that I've seen before include "Provide supporting evidence, make definite" , "Make (provisional arrangement) definite" , "Ratify; establish" , "Corroborate" , "Substantiate" .)