Every once in a while I come across a case where a customer is complaining that every cable they test is failing. The first thing they do is blame the tester. Recently I was at a site where this was happening.
I've learned the first thing to do is make sure they are using the correct cable type and test limit. Remember, these both need to be set to the correct values. If you set the cable type to Cat5e and then leave the test limit at Cat6A, all of your Cat5e cables are going to fail.
To get the most reliable and repeatable test results, be sure to set both the Cable Type and Test Limit to the appropriate settings for the cables your are testing.