Supply less well-off dealer (11)
I believe the answer is:
stockbroker
'dealer' is the definition.
(I know that stockbroker is a type of dealer)
'supply less well' is the wordplay.
'supply' becomes 'stock' (stock can mean a supply or reserve).
'less well' becomes 'broker' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'stock'+'broker'='STOCKBROKER'
'off' acts as a link.
Can you help me to learn more?
(Other definitions for stockbroker that I've seen before include "Buyer and seller of securities for clients" , "Agent for buying and selling securities" .)