Structure problems will most often come with more than one clue, doors that don't work right or don't fit right. Foundation issues that can be seen, rot in structure just above the foundation. If the ceiling has a new sag, you can check for a broken joist by gently pushing on the ceiling or inspecting from attic. Has the floor developed a new slope.
If you keep coming up with no for all that it is just a crack in plaster.