What you will notice
A sinking foundation rarely means the whole house drops evenly. One corner, one side or one wall goes down while the rest stays put. That uneven drop shows up as:
A corner that looks low
The slab edge at one corner shows less concrete than the others, or the brick line dips.
Cracks that point toward one spot
Wall, brick and tile cracks all seem to run toward the same corner.
Floors that slope toward one side
A ball rolls to the same part of the house in every room.
A gap at the top of the wall
Drywall pulls away from the ceiling on the low side.
A porch or patio pulling away
The step or slab no longer meets the house.
A chimney leaning out
The chimney footing sank on its own.
Doors that stick on one side of the house
The ones on the low side bind first.