It was so rare to find a shop-keeper that sold books that was genuinely excited and enthused about them enough to make meaningful recommendations; it was in part one of the reasons he had stopped visiting Flourish and Blotts - their core business was in the school trade, and while they could source books and tomes (and even grimoires) on request, there wasn't really that much desire to know what was out there enough to really make meaningful recommendations.
The shop-keeper's question threw him for a moment and he blinked. He could hardly say the truth - that he had been something of a researcher and a scientist for the Department of Mysteries, even if it were true, and had been a major catalyst in his studies of the field, but he collected himself and smiled politely. "I do sort of work in the field; I teach the subject at Hogwarts at present, but the level on the syllabus is, if I may be bold, quite foundational. Good for progressing into deeper studies somewhere else, but I rather found a lack of further reading to be quite the frustration."
He lowered his voice, almost conspiratorially. "The Hogwarts library has a great many books but very few on arithmancy, and almost nothing on contemporary research and theory. It is a very pleasant place to read, but quite inadequate for research."
Harold turned to the woman - he still hadn't quite placed what her situation within the establishment was, whether an assistant or a friend - and was about to thank her for her suggestions when she answered his questions for him, explaining that she was a wandmaker, across the road, and that she would make him a beautifully bespoke wand. He wasn't, at that time, in need of a wand, but he resolved that he would pay her a visit next time in town, just out of polite curiosity if nothing else.
He was surprised to note that both of them talked about magic mirrors - the shop-keeper himself mentioned having had a delivery of them, and the wand-maker was clearly bubbling with a peculiar sort of curiosity.
He took his glasses off and polished them with his tie. "A magic mirror, you say? Well, my first thought would be to study the refractive properties - how much of the mirror is rather just that: a mirror. Every mirror I have ever seen still contains quite an amount of the essential..." He couldn't place the word he wanted. "...mirrorness, I suppose you might say. Even if enchanted to show your heart's desire, your innermost love, your worst nightmare, your past, your future, it still is quite rooted in a reflection of you as its beholder."
He pushed the glasses firmly back on his nose, almost pinching at the bridge, such was his enthusiasm. "I'd be perfectly happy to take a look at a mirror, if you have a particular one you are curious about, and tell you what I can see from it, if that would be of interest?"
A wry smile crossed his face and he spoke with a tone of amusement. "I have the privilege of teaching a classroom full of slightly bored sixteen year olds how to inspect magical artefacts - we do not usually cover mirrors, as they can be subtle and deceiving, but perhaps I should get them into year's O.W.L. examinations..."