There is no way to know, t hough without health testing. It's just a fact. A dog can have bad h ips and live a normal life, but pass those bad genes on to the next generation. There are lots of recessive diseases as well. Without doing the tests there is no way to know if those genes are in the bloodline. Mix 2 unknown bloodlines and who knows what you can get. It could be something as minor as missing teeth or as major as a cleft palate. What about puppies born with hernias? Those are genetic as we'll, though an over-enthusastic mother can as well.
Also, don't take "oh the vet said the hip xrays pass" as gospel. Unless you go to an orthopedic specialist, a vet isn't going to have the experience with your particular breed to give a thorough opinion.
The same applies to "oh the vet said they are healthy". That is like the elderly man who refuses to go to the doctor because he doesn't think he is sick. If you don't have any tests done, then you only have assumptions.
Temperment is more than just "mean". There is fear, prey drive, aloofness, too friendly, recovery from a startle, reaction to new people/places/things, and on and on. All of those thing have a genetic element.