9S thinks about that really hard. Like really, really hard. Androids engaged in trade with each other, but that's because they were disparate groups with different needs. But more importantly, Yuya seems to be saying that by not paying the money, other humans wouldn't be able to enjoy the arcade.

And that would be bad!

He'd only been thinking about how Yuya, a human, shouldn't need to spend money on his behalf, not about how the human run arcade needs that money!

Oh no. Oh no. He'd taken that trip with Childermass, and...

"Oh no." The distress distracts 9S enough that he messes up the next few notes. "I went with the Aquisitioner to one of the electronics stores..."