Any test in which you have control over any of the elements is invalid. The protocols of ABX blind testing remove the subject's ability to "fool themself" into thinking they sense something that they don't.
The statement , " .... nothing is perfect in this price range ..." has nothing to do with the issue, because perfection is not the issue. The issue is whether the DUT performs at a level below the threshold of human perception.
The statement was made that all competently-designed amplifiers sound the same when operated below their threshold of clipping. Blind ABX tests have, to the best of my knowledge, confirmed that. If you can identify competently-designed amps in a blind ABX test, I'm sure there are many people in the scientific community who would show great interest in you.
Identification of a DUT in a test other than blind ABX is a red herring. Jim Taylor.