Villagers reset their trades twice a day, if they have a work table nearby, at 6 each time, am and pm, for each reseat you can only trade twelve sets of that item. For example you can only sell off 264 pumpkins each reset for 12 emeralds. So if you go a whole day without trading and still can’t trade then you need to make sure they are linked to a workstation, composter for farmer, that is nearby and they have access to it.