Charge too much for a gloss finish on wood (4)
I believe the answer is:
soak
'charge too much' is the definition.
(I've seen this in another clue)
'gloss finish on wood' is the wordplay.
'finish' says to take the final letters.
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'wood' becomes 'oak' (oak is a kind of wood).
The final letter of 'gloss' is 's'.
's'+'oak'='SOAK'
'for a' is the link.
(Other definitions for soak that I've seen before include "Get wet" , "Steep in water" , "Saturate" , "Immerse in liquid" , "Make thoroughly wet" .)