It takes a good deal to satisfy him (6)
I believe the answer is:
trader
'it takes a good deal to satisfy him' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'satisfy him' is the wordplay.
'satisfy' becomes 'tra' (I can't explain this - if you can you should give a lot more credence to this answer).
'him' becomes 'Der'.
'tra'+'der'='TRADER'
Can you help me to learn more?
(Other definitions for trader that I've seen before include "Red tar (anag)" , "Person in the business of buying and selling" , "Merchant ship; dealer" , "Dealer, monger" , "One selling" .)