The barring of Jews from guilds (established by shopkeepers to protect against competition) made it impossible for Jews to have storefronts. This exclusion prolonged the history of the traveling Jewish trader who peddled goods door to door from a knapsack or wagon. “Protected” Jews though, made enough of an income to set up homes and continue their livelihoods as clerks for the municipalities. You will see the same pattern when Jews came to America. If the stories of your ancestor are that he sold goods out of a wagon, it could be that the family had survived through the decades and perhaps centuries, dependent upon that livelihood.
Suellen Ocean is the author of Secret Genealogy a how-to for tracing ancient Jewish ancestry and the historical novel The Guild available at Amazon, B&N and Ocean-Hose.