From PSA's website:
The Advantages of PSA Grading
PSA provides expert analysis and protection for your collectibles. Using state-of-the-art, proprietary methods, the hobby's most astute and knowledgeable grading experts render carefully considered, unbiased third-party opinions of grade. When you see a card/ticket in a holder displaying the PSA logo, you can be confident that the card/ticket has been properly authenticated and graded by the experts at Professional Sports Authenticator (PSA). These are some of the attributes that have made PSA the largest and most respected third-party grading and authentication service in the world.
http://www.psacard.com/About/WhyPSA
I highlighted the word "confident" because the foundation of any con game is confidence. When people like myself have openly complained about doctored cards getting past the graders with credible proof, PSA has taken a very aggressive adversarial position against myself and others such as banning us from their message boards and club memberships and nothing has obviously been done to address the problem.
At what point does proven incompetence with no diligent attempt fix the problem encroach actions of fraud? What about causes of action such as gross negligence for failing to fix a problem that you are aware of or unjust enrichment which is unjustly profiting from fraud? As I've said many times before, you don't have to have purchased a doctored card to be a victim; card doctoring devalues good cards by artificially inflating the supply of the same cards.