NanoVNA was calibrated using the calibration kit that came with it. I then measured S 11 over the frequency range from 10 to 200 MHz. I connected each cable to the (50 Ω) NanoVNA CH0 on one end and a Z ref = 50 Ω calibration load on the other end. This article goes into the details of how to measure characteristic impedance of a transmission line. Since this is something that is not trivial for the customer to measure and a 75 Ω cable will sort of work even in a 50 Ω system I guess it's easy for sellers to get away with this kind of scam.
I've recently found out that BNC coaxial cables sold as having a 50 Ω characteristic impedance often are in fact 75 Ω. I guess by now everyone is already aware that cheap no-name items often aren't what they claim to be.
