@OP - Quite a revealing response to my question.
So - by your own admission, as your attempt to listen for differences between cables was inconclusive due to a salesman's reported intervention, you do not know on any empirical basis as to whether different cables sound different.
Your response continues with a number of logical fallacies. "You can go ahead and call me a liar" "my beliefs are my own" - ad hominem and red herring fallacies".
The rest of the post is an argument from authority fallacy - "I say it, therefore it must be true".
For the record, I did not express any opinion as to whether different ethernet cables sound different. But I keep an open mind on everything related to audio.

