Use Observer, Wither Skeleton Skull, Crafter to craft Auto Trade Cap at the Smithing Table.
Using Dispenser to put Cap on Villager allows for automatic trading.
Place Container on top of head of Villager, And provide the items they buy, Traded items will drop.
The first slot of the Container corresponds to the first item Villager buys, and the second slot corresponds to the second item.
Only the first trade line can be automatic traded, And immerse the Villager'legs in fire to cycles through the trade list.
The lited Redstone Lamp under Villager's feet can stop auto trading.
