Expert in good shape to make money (6)
I believe the answer is:
profit
'make money' is the definition.
(I've seen this in another clue)
'expert in good shape' is the wordplay.
'expert' becomes 'pro' (short for professional).
'in good shape' becomes 'fit' (I've seen this in another clue).
'pro'+'fit'='PROFIT'
'to' is the link.
(Other definitions for profit that I've seen before include "returns" , "Clean up" , "Gain, return on investment" , "Use" , "Gain from employment of capital" .)