The London leather market inherited an age-old regulation framework. But some harsh disputes among the leather trades in the Eighteenth Century re-activated the debate about norms and rules. Disputes between butchers, tanners and curriers revolved less around the principle of the quality control than around its intrinsic definition, leading to a significant shift: the former definition of quality as an absolute, defined by precise norms (which I call “regulated quality”) is challenged by a more flexible definition, the “deliberated quality” established by a jury formed by representatives of each trade. Hence quality turns out to be a pure convention, grounded on a deliberative process. This case study, by approaching norms of quality and certification process from the point of view of the actors of the market instead of adopting the former cliché of free-market versus regulation and control, sheds light on the need to set a new ground to discuss these issues.