The Breed Mean Score is 19, which is fairly good and although a dog may appear lame, only scored xrays can confirm the actual score and whether it is HD or some other condition. No-one can just look at a dog and say it has HD, although as I said before a good vet can read an xray plate and give you an idea.
On the other hand, some dogs can appear fine and yet get a high score, as their bodies can compensate and their muscles build up to support the poor hips. I had a GSD who could jump fences and into the car without a problem, and I was planning to breed from her. When she was xrayed the vet said they looked pretty bad and sure enough when they came back she had a score of 78 so was never bred from, although never suffered from any form of lameness.