Quest Giver

How lax must the cleanliness be in a building to attract giant dire rats into the basement?

Giant rats in the cellar. It’s such a common quest to be almost mockable. A trope. But it’s so very handy, being a simple quest with low risk combat that is quick to complete and takes place in an urban area, allowing you to complete the quest and rest in rapid succession. It’s rare to see a wolf or bear in a city, but rats are common and familiar. And rats don’t need to be explained to new players like stranger monsters: no extra motive or description is needed.  

But what happens when the rats get tired of being hunted down by low level adventurers?