"Please," Vayj says off-handedly without looking up or noticing the humans, "There is no reason to get riled up. I'm a magister; I like examining interesting magic, and your father's work is excellent. I've paid for my drink already, and I'm using the purchase price to do some experiments."
"See, no harm done...unless...I was working under the assumption that the glasses' ability to produce any comestible substance meant that it was merely conjured from the air by magic. Could it be that instead the magic of the glass conjures up some sort of reagent or something from the cellar and transmutes it into the desired food? I'll admit the workings of the item were something I was trying to discover but failed, not something that happens too often in my examination of magical phenomena. I was under the impression that my studies in wasting some of the drink weren't costing you anything, else you would not have made the meal an all-you-can-eat bargain, but if I was mistaken, then I humbly apologise. Could you let me know how it works? Could I talk to your father about it? I'm curious, is all. Glirael, goddess of invention, knows that if I understood the workings properly, perhaps I would be able to engineer a way for you and your father to increase your profits a thousandfold. Much as I hate to admit it, I know some people involved with the skyships, and if you could produce unlimited supplies of food and drink from these glasses, and then ship them across the lands via skyship, you could replace the chain of supply of the whole kingdom's farmers..."