Well he is a merchant at first so he sell portion of meat and other itemsto the merchant and other guild so i guess... Soone or later the adventure guild will have trouble since he is newly registered as adventurer
since he takes all the meat, he probably takes even less profit than he would originally be getting, and the demand for these items are probably really high since they come from monsters that are hard to fight and kill.
Remember that his hunted preys were always reported to the lord of the place so its not just the guild paying but more like the territory itself. I'm sure the lord pays parts of it specially those designated quests.
How is the mc not bankrupting the guilds? Dude always brings the rarest and most powerful creatures to the guilds, and not only one or two, but dozens because of Feru— repeatedly on the course of several days. I can't really believe that all the guilds have so much money, especially the ones in small towns.