Something to save sanity for the poor merchants:
A letter of trade bought from the Peer council that allows free use of the stalls, or greater ease of renewal, or both. For some reasonable sum (say between 500 to 2000 groats) the merchant gets a letter that lets them use the stalls without paying a fee. If possible, it might also allow for a preset message that will be used automatically upon renting/renewal. Or maybe it could extend the rental period to one hour. Could that be done?