"I appreciate both the effort you made and the offer, but I think I'll be okay without you replacing my tea," Luke answers with a laugh. "If anything it should be Magnus replacing it, but you know he's only steal some from a store somewhere and magic it into my cupboard and then I'd feel guilty knowing it hadn't been paid for."

He's partly joking, but partly serious, too. Magnus has told him more than once that he can't just conjure things out of thin air, which means if there's suddenly a bunch of new tea in his cupboard that hadn't been there the moment before, they'd still come from somewhere. And then Luke would feel like he had to pay for it all.