I don't envision a dealer allowing someone off the street to bring cables, sit back and allow multiple hookups by a rookie. Not gonna happen. I call B.S. It doesn't help that the OP brags of his serial duplicity.
The test conducted by the OP was inherently incapable of demonstrating what was claimed, that the three different cables did not have different sonic properties. What happened in the story is equitable to what happens at shows when someone moves brass bowls around or puts a weight on a SS component. Half the time audiophiles are convincing themselves they hear a change when it's at best marginal or inaudible. He basically showed that neither his (by self-admission), nor the dealer's ears are to be trusted. That is all the OP's story demonstrates. Because there was no actual swapping of the other two cables the incident cannot demonstrate the three cables sounded the same. It literally has the same lack of testing validity as persons who claim all power cords sound the same but have only used one type.
Note that because the OP could not hear the differences between cables he used a test which set out to prove there was no difference. Hmmm... no bias in that, huh. OOPS! One problem, only one cable used! Just a SLIGHT oversight, as drawing a conclusion on something you have not tested (the other two cables) is called an opinion, not a conclusion! If not fabricated, the account was about a test borne out of ignorance, duplicity, and arrogance rather than sensibility.
For the OP to buy the expensive cable seems in character; deception. :(