Master of Trade to upgrade weapon ?

[Julien Dien]

One of my PC use Master of Trade to upgrade his mwk Composite longbow to +1 Composite longbow. He only costs 900 gp. Is it ok?
I'm not sure if the upgrading is "a single purchase" or "buying"?

PSFG 19 wrote:

Master of Trade(Fame 20, 4 PP) Using faction contacts and mercantile experience, you can always get yourself the best deal when buying goods. Once per game session, you may make any single purchase you could normally make at a 10% discount. This discount is not available on spellcasting services or material components.

[Julien Dien]

I found the answer in Organized Play Legacy FAQ. Master of Trade can not apply to upgrading magic items.