Engineers and real estate inspectors are in the business of informing potential buyers as to the condition of the house, not its marketability. However, there are a couple of points that bear on this question that can best be made by an engineer or inspector:
It is unreasonable to not expect some degree of damage due to foundation movement in resale houses in the Greater Houston Area. The combination of expansive soils, thin flexible slab-on-ground foundations and wooded lots virtually guarantees that many houses will experience some damage due to seasonal foundation movement. This type of movement rarely affects the structural stability of the frame structure of the house.
There is a wide range of opinions concerning how much cosmetic damage is acceptable or not acceptable. Some people find even hairline cracks unacceptable; others find almost any crack width acceptable so long as there are no structural safety or stability issues. If the degree-of-damage shown by a house you are considering buying makes you uncomfortable, you should probably not buy the house.