Huge margins on suit paid for by Charles (8)
I believe the answer is:
stonking
'huge margins on' is the definition.
I can't tell whether this definition defines the answer.
'suit paid for by charles' is the wordplay.
'suit' becomes 'st' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'paid for by' becomes 'on' (as in 'the drinks are on me').
'charles' becomes 'king' (Charles I or Charles II).
'st'+'on'+'king'='STONKING'
Can you help me to learn more?
(Another definition for stonking that I've seen is " Very large".)