Common fee is what coals do? (5,4)
I believe the answer is:
going rate
'what coals do?' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'common fee' is the wordplay.
'common' becomes 'going' (I can't justify this - if you can you should believe this answer much more).
'fee' becomes 'rate' (I've seen this in other clues).
'going'+'rate'='GOING RATE'
'is' acts as a link.
Can you help me to learn more?
(Another definition for going rate that I've seen is " Prevailing price".)