Possible Clues:

• I daren't exchange one car for another
• As part of deal, exchange low grades in school
• Lower classes in coach give something as part payment
• Give as part payment
• New car price offset
• Trained (anag.)
• How the editor turns up in the railway for the exchange
• Following notes in following part-exchange
• Part-exchange business fashionable
• Tried an alternative exchange for second-hand article