Positive results for a single test, on the other hand, are more credible since positive results were obtained in spite of any problems or errors that may have occurred in the test.
Most blind tests are simply to hear a difference. So you are defining positive results as one where the user heard a difference and we are sure there was no error that produced an audible difference where there otherwise would not be one. But if you knew there was operator error, you'd throw out those results, so, if there's error, it's unknown by definition.
I would describe both a)hearing a difference due to unknown operator error, as well as b) the well supported bias towards hearing a difference* as false positives, and difficult to quantify.
Anyway, legit or false, positive results (blind tests of cables, amps, hi-res vs redbook) remain vanishingly rare, so there's not much to be credulous over.
* See the Stereophile tests in the link, particularly the devastating footnotes, for a hilarious read on this.