Subjective Tolerance Levels
First, the good news: assuming the house is a couple of decades old (or older!), the settling is very likely historic.
So, for a home that was built in say, 1925, the settling likely occurred (and stopped) by 1927.
The bad news?
It’s (very) hard to correct.
It’s possible to use floor jacks ” but those risk doing severe damage.
Repairing a foundation, meanwhile, can cost tens of thousands of dollars, and even then there’s no guaranty.
“Settling for Settling”
Instead, I tell my Buyer clients to decide whether the settling is something they can live with.
Practically, if they notice settled floors immediately upon entering a home (vs. my pointing them out) . . . I recommend they keep looking.
P.S.: pronounced settling can also be relevant if the home is a prospective tear-down.
That’s because settling suggests soft(er) soil, a high water table, or some other condition which can require pilings to correct.
That adds to the construction cost ” and subtracts from the lot’s value.