If you max out a trade with a villager enough so that it restocks twice, something the game reminds you is the max when you try to trade again, you can glitch it so the villager still trade. It's simple: unload the chunk the villager is in, by either flying away, walking really far, or if you're on a server teleport away. I have not tested if it works with the nether portal. I have only tested it with a render distance of 11, I do not know if it works on lower render distances.