Somehow trained in part payment (5-2)
I believe the answer is:
trade-in
'part payment' is the definition.
'trade in' can be an answer for 'part' (I have seen 'part of exchange' mean 'trade in' so perhaps 'part' could also mean 'trade in'). I'm unsure of the 'payment' bit.
'somehow trained' is the wordplay.
'somehow' is an anagram indicator.
'trained' anagrammed gives 'TRADE-IN'.
'in' is the link.
Can you help me to learn more?
(Other definitions for trade-in that I've seen before include "Article used in part payment for another" , "Something used in part exchange" , "Old item given in part payment for a new one" , "Article used in part-exchange" , "Trained (anag.)" .)