A quote from Foundations in Expansive Soils published by the Army Corps of Engineers:
Most slab foundations that experience some distress are not damaged sufficiently to warrant repairs.
I frankly find this ambiguous so I am going to rewrite it with a view to make it clearer.
Most homes with slab-on-ground foundations, even those that show some foundation related distress, are not damaged sufficiently to warrant foundation repair.
Notice there is no reference to elevation measurements or floor slopes. It is damage to the house that warrants foundation repair, not the degree to which the slab is not level.
I sometimes get some pushback concerning this
The average person expects and prefers that a floor in a house be level. I understand that and when the floor is not as level as normal, I report it, but I do not recommend repair just because the foundation is not as level as someone might like. The levelness of a slab foundation is an aesthetic issue, not a structural, load carrying issue. When houses have foundations that are, say, three inches or more out of level, you are kidding yourself if you think a foundation repair contractor will make it much more level without risking serious structural damage to the house and the foundation.
If you cannot tolerate the floor sloping in a house that’s for sale, I recommend you find another house that suits you better.