Crossword Genius

By mentioning a purchase (3)

Ross

I believe the answer is:

buy

Here is my best explanation:

'a purchase' is the definition.
(buy is a kind of purchase)

'by mentioning' is the wordplay.
'mentioning' shows a homophone (sound like) (I've seen 'mentioned' mean this).
'by' is a homophone of 'BUY'.

This clue was last seen in Evening Standard