My guess is that it's from the state, and not as a particularly special case. Just another thing taxes can be allocated for, assigned whenever they get reports of monsters reaching 'problematic' rather than 'nuisance'. Like road maintenance.
How plausible that is depends on how often these guys run that scam, and how much effort they put into faking the evidence.
When you think about it, the guild is funded by taxes and employs adventurers to do tasks that the kingdom can't spare its own military and labor force to do, such as keeping the monster population down and collect raw materials. Remember what happens when the so-called Hero Group overhunts the monster population in an area. They create a huge void of monsters and materials, so now those adventurers are denied their livelihood. As a result, with so few monsters to hunt, the adventurers move away and thereby causes a labor shortage. What's worse is that the monsters that are stampeded towards areas that don't have enough adventurers to handle them all.
The village is cheating the system of rewards and ranking up for adventurers. By falsifying monster subjugations, the adventurers are able to rank up without much effort. For the mayor and other conspirators, they get back the tax money they paid out to the state and a bit more. So in the end, it's the state and guild who are losing. Naturally, since the hunters go into the forest, they know there isn't any danger, but they have no choice but to keep quiet, or they'll be banished.
When the goblin threat became real, the hunters thought, "TO HELL WITH IT! I WANNA LIVE!" So they asked Sarto's guild for help since they have legitimate C-Ranks and higher. Of course, the mayor doesn't want his scam to be exposed, so he paid the cancelation fee and is just hoping the goblins will go away.