Sale of lead varies (4)
I believe the answer is:
deal
'sale' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe there's a link between them I don't understand?
'lead varies' is the wordplay.
'varies' indicates anagramming the letters.
'lead' is an anagram of 'DEAL'.
'of' is the link.
Can you help me to learn more?
(Other definitions for deal that I've seen before include "Distribute (cards); wood" , "Act of business" , "understanding" , "Large quantity (of wood?)" , "Loss of life" .)