More often than not, the labs that test athletes for performance-enhancing drugs are fairly reliable and credible. Very rarely will these labs mess up test results since they exist to provide reliable testing time and time again for professional sports leagues. Of course, these labs need to be vetted and audited from time to time.
The laboratories that test athletes are credible and reliable. The problem is that athletes are the ones cheating. There are stories of how cyclists in the Tour de France get whole-body blood transfusions to cheat doping tests. Surely there are ways NFL, MLB and NBA players cheat drug tests on a regular basis.
Athletes are constantly racing to fund people to keep them ahead of the tests with new drugs that can't yet be traced, so how reliable these labs are only goes so far. With that said, I don't doubt their credibility, there have been a few chumps out there that haven't done the right thing but for the most part they have been on point.
I believe that the athlete testing laboratories, the ones that test for drug abusers in professional sports, are reliable. Despite what Ryan Braun, a guilty cheater, would want you to think. These labs have their integrity to protect and they wouldn't risk it just to help a few cheaters prosper.
I believe the laboratories used to test athletes for performance-enhancing drugs are credible and reliable. As with any drug test, there will always be people who want to try to beat the system or cheat the test. Sometimes people achieve this feat and it should be expected. However, the labs involved should not be held responsible for people who continually try to cheat the system.
The laboratories used to test athletes for performance enhancing drugs are not always credible and reliable because athletes still get away with using the performance enhancing drugs and still continue using the drugs. There needs to be a better way of testing in order to get athletes to truly stop using the drugs.
While I am sure that the laboratories that test athletes for performance enhancing drugs have stringent requirements, the drug tests themselves have error rates which allow for false positives and false negatives. Combined with the constant possibility of human error, it is unfair to rule on an athlete based upon a single test result.