"I should have maybe checked this first but does anybody here besides me have a specific amount of G that they actually... have.  Mine is 500G, left to me by Grandpa--is there anyone else who can say what theirs is?"

"Gosh. Maybe... not? I feel like... I can check? But it's just zero?"

"Emily, is there anything you can try buying from Gus that you'd be able to sell back to him at the same price?"

Emily goes around to the customer side of the register.

"I'd like a salad, please, Gus."

Gus hands her a salad.

"How much G do you think you now have, Emily?"

"Um... zero? Apparently?"

"Try selling him back the salad."

Emily grabs the plate of salad and starts walking back to the bartender side of the bar with it.

That doesn't look like what he thought he was asking Emily to do, but also Oliver is new here and will wait to see what eventuates.

"Gus, go to the customer side! I want to sell you this same salad!"

"Pause!  We're doing better than I expected, but that wasn't quite what I meant!  Would Gus buy a salad from me if I wanted to sell him one?"

"Now why in the world would I want to buy a salad? Of course not."

"Is there anything you do buy?  And also sell."

"I don't buy things at all! Pierre does though, he'll buy lots of things."

"And I buy ores and gems and suchlike at my blacksmith shop!"

"I believe I've seen Willy purchasing caught fish."

"Emily, you've been seeming like a remarkably sensible and dare I say self-aware person, around here.  And you'll notice, I hope, that when you bought that salad, the amount of G you had went from 0 to 0, so it didn't hurt you, actually, to buy it."

"What if I were to--actually, this might be easier to do than to ask permission for.  Emily, can you leave the salad on that side, and come around to the customer side?" 

"All right!"

Emily does not normally enjoy this job this much, usually it's just a way to pay the bills.

Emily notices that she feels confused about her previous thought, but shakes it off.

She drops the salad on the floor behind the bar and goes around to the customer side as requested.

Oliver, if nothing prevents him from doing so, will go around to the bartender side.  Does this operation succeed?

It does!

Next!  Pick up the salad!  Does that work?

Oliver picks up the salad!