Craft shops could specialize in order to increase efficiency of production. They could also sometimes get very big, and benefit from an economy of scale, and if there were trade routes and trade agreements, there could be a very big market for what they produced. In the 18th c., fine scythes were made in Austria, fine pocket watches in the Jura, and both were exported widely. A good very early example of this might be the African red slip ware ( sometimes abbreviated as ARS) produced circa 1st-7th c. AD in what's now Tunisia and exported widely within the Roman empire . Using one technique, one kind of clay, one kind of glaze, and using some very large kilns resulted in what was obviously a very large output for a very long time. But, how often this sort of thing would occur, over a thousand years or so, compared to local craft production might be kind of hard to definitively answer. It might be enough to say that, as there were still mostly human energy sources, human muscles, doing a lot of the production of things, and a lot of labor involved in transporting them, the prices were still significant. So, a small local shop could still often compete with a far-away big one, especially for large things of relatively low value: the farmer in Gaul might well own some ARS, but likely his ladder was made locally.