Minecraft wiki entry for Trading, associated text: The price of an item rises and falls depending on three factors. Items with a high price multiplier (0.2) are affected by these changes more than items with a low multiplier (0.05). All price fluctuations affect only the first item involved in trade; for example, for an initial trade of 32 sticks for 1 emerald, the price might be driven down to 1 stick or up to 64 sticks for 1 emerald, but never for 2 emeralds. Additionally, no quantity can go lower than 1 or higher than the stack size.