In 1.21.11, novice armorers buy 5 iron ingots for 1 emerald when Villager Trade Rebalance is enabled. In 26.1 Snapshot 1 (i think, i haven’t actually tested that version in particular but it definitely is different in snap2 and snap3), this was accidentally changed to trading 5 iron ingots for iron boots.
MC-305743
When the "Villager Trade Rebalance" experiment is enabled, novice armorers sell iron boots for 5 iron ingots.
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The attached screenshot also demonstrates that Villager Trade Rebalance armorers have the non-Villager Trade Rebalance trades in 26.1-snap3, though I don’t know if the rest of that was fixed with MC-305675.