This command summons a Villager who buys Poisonous Potatoes and sells Potatoes, Baked Potatoes and Emeralds
Put it in a command block

Java Edition 1.18
/summon villager ~ ~1 ~ {VillagerData:{profession:farmer,level:3,type:plains},PersistenceRequired:1,CustomName:"\"Poisonous Potato Trader\"",Offers:{Recipes:[{buy:{id:poisonous_potato,Count:1},sell:{id:potato,Count:1},rewardExp:0b,maxUses:1000},{buy:{id:poisonous_potato,Count:2},sell:{id:baked_potato,Count:1},rewardExp:0b,maxUses:1000},{buy:{id:poisonous_potato,Count:3},sell:{id:emerald,Count:1},rewardExp:0b,maxUses:1000}]}}

Java Edition 1.17
/summon villager ~ ~1 ~ {VillagerData:{profession:farmer,level:3,type:plains},CustomName:"\"Poisonous Potato Trader\"",Offers:{Recipes:[{buy:{id:poisonous_potato,Count:1},sell:{id:potato,Count:1},rewardExp:0b,maxUses:9999999},{buy:{id:poisonous_potato,Count:2},sell:{id:baked_potato,Count:1},rewardExp:0b,maxUses:9999999},{buy:{id:poisonous_potato,Count:3},sell:{id:emerald,Count:1},rewardExp:0b,maxUses:9999999}]}}

If you play another edition, please comment
No Bedrock Edition