Since you are the keeper of the graveyard in Graveyard Keeper, one of your tasks is butchering corpses. This brings in meat that can be sold to the Dead Horse Tavern, but requires a special meat seal (stamp) to sell.
The first way to get such a stamp is to raise the graveyard rating to 5 in order to open a church. This will allow you to access the Royal Services box right outside the church door. Here you can buy a seal for 50 silver coins, but before that you must acquire the title of "Citizen" for 50 copper coins.
The second way to get the stamp is to talk to the NPC "Snake" (Snake), which is located behind a closed passage near your basement. Talk to him and complete several tasks for him to increase your reputation along with his to at least 30, after which he will give you a certificate for free.
Keep in mind that at least two of Snake's quests take place in the Dungeon, and he himself can only be found on the days indicated by this symbol 
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