Your idea is to buy anything if a user want from g2a.com etc site and gets bitcoins from the users instead of fiat.
If you don't charge extra fees then it is a great idea .
Yeah you get the point. And if I wanted to make it a non-profit business then I guess I would provide the receipt of the transaction to my buyer. Making it fair.
No need to provide the transaction. The user just wants the game just give the user cheapest rate from around you can have profit too .
Example, You are getting a game for 10$ instead of 14$ from steam you can sell it for 12$ and still have 1$ profit.
Good luck!