Dodgy dealer finally sells tap with drip (4)
I believe the answer is:
spiv
'dodgy dealer' is the definition.
(I've seen this before)
'finally sells tap with drip' is the wordplay.
'finally' indicates one should take the final letters.
'with' means one lot of letters go next to another.
'drip' becomes 'IV' (intravenous drip).
The last letters of 'sells tap' are 'sp'.
'sp'+'iv'='SPIV'
(Other definitions for spiv that I've seen before include "Black market operator" , "Unscrupulous dealer" , "WW two black-marketeer" , "Flashy black-marketeer" , "Timepiece" .)