In July 1470, Louis XI granted Jean VI Malet de Graville permission to hold an annual fair at Châtres-sous-Montlhéry. From institutional, legal, and economic perspectives, nothing seemed to prevent the establishment of this commercial gathering in the south of Paris. Yet in April 1471, the letter patent establishing the fair had not yet been recorded by the royal administration, which ordered a de commodo et incommodo survey in order to inquire about the legitimacy of the request and to define Malet de Graville’s rights and franchise. The applicant (who was a prisoner of Edward IV in London) and his son Louis then began a struggle with the French king and his administration that was to come to an end in 1475 when Louis XI imposed the partial endorsement of the patent letter. The archival records of this affair, which are exceptionally well preserved, contain the survey ordered by the provost of Paris and the letters exchanged between the protagonists in the endorsement request. It shows an administration keen on preserving the royal domain as well as its own privileges and reveals the underlying conflicts of interest, even the political and economic issues at stake when a privilege was granted by the king.