Minecraft wiki entry for Trading, associated text: The first image of the trading system released by Jeb. The currency item (later updated to the emerald) can be seen in the inventory.
An enhanced version of Jeb's screenshot showing the original ore texture more clearly.
The trading menu before Bedrock Edition 1.11.0.
Trading options of a master-level weaponsmith.
An unemployed villager refuses a player trying to trade.
A nitwit villager refuses a player trying to trade.
A Villager presenting the emeralds.