Each patch panel port should be verified and certified by the installer as part of the contract. You should also have cable testers, both Cat5 and fibre, available in the data center. With these you can verify that the patch-panel ports were done correctly and, if you have questionable cables, you can find out whether they are good or not. This helps to eliminate doubt.
The ability to verify cables and ports is core to the design. That's why the quote “…when you have excluded the impossible, whatever remains, however improbable, must be the truth” is at the top of the “Data Center Design Criteria” chapter.