Looks? Many people are conditioned to like the near death look of royalty through association with wealth and power. Does a defect in the observer's taste make the observed not bleed to death?
Anemias such as sickle cell and malaria are the text book example. Having two parents from the same area means high frequency of them having the same gene. The same sickle cell anemia gene makes one quarter of their children fully anemic and leaves one quarter unprotected from malaria. One such parent makes half of children protected and half unprotected.
Anyone can breed on the dominant traits of genes and talk about looks. Their results are defective because of recessive traits. Thus a first mutt with their line has much higher odds of being healthy even if it's other parent is also inbred. But two cross breeds from those same lines are going to be more likely to produce unhealthy offspring again when compared to fuller mutts.
