Oz smiled. "I'll let you know." Oz could say a lot of things with a smile, which was a good thing since he didn't say very much at all. It rubbed some people the wrong way, and others took it in their stride. Women especially seemed to think he should say more than he did. Judging from her scent, Oz wasn't entirely sure this person was a woman at all, so maybe her perspective would be different.
After the pause he added, "It's okay. I've had a lot of practice." This smile was benign and accompanied by a soundless little laugh, all of it reassuring to a would-be pharmacist.