Barter shops allow users to trade items using ingame items as the currency.
The layout for a shop's sign is as follows:
Before creating the sign you must first place a chest, trapped chest, or barrel underneath. This block will act as the inventory for the shop and is where you will place your products and where the traded item will go. The image above is an example of a shop that sells 1 iron ingot for 1 redstone dust.
The names of the items are based on the names that Minecraft uses internally. If you are unsure of the name of an item you can find it using this website: https://www.digminecraft.com/lists/item_id_list_pc.php
To use the shop you simply right click the sign while having enough space in your inventory for the new items as well as enough funds to be able to pay for the item.
Because of the switch from ids to namespaces for items I know some item names will not fit on the sign. As a fix for now, certain namespaces have aliases that can now be used instead. If a sign uses an alias and you can't figure out what it is, you can shift right click to see the full names of the product and cost.
The aliases are as follows:
Prefixes: * acacia_ : a_ * birch_ : b_ * cobblestone_ : cbl_ * cooked_ : c_ * dark_oak_ : do_ * dark_prismarine_ : dp_ * end_stone_ : es_ * firework_ : f_ * jungle_ : j_ * music_disc_ : md_ * oak_ : o_ * red_nether_ : rn_ * red_sandstone_ : rs_ * smooth_sandstone_ : ss_ * smooth_red_sandstone_ : srs_ * spruce_ : s_
Suffixes: * _banner_pattern : _bp * _concrete_powder : _cp * _coral_block : _cb * _coral_fan : _cf * _fence_gate : _fg * _glazed_terracotta : _gt * _pressure_plate : _pp * _shulker_box : _sb * _spawn_egg : _se * _stained_glass : _sg * _stained_glass_pane : _sgp * _terracotta : _t