Buyer Beware

This is my first post on Audiogon Forum but I have been a audiophile for almost fifty years. I like to buy and sell used equipment because it gives a chance to try a much wider range of products. Recently I wanted to try different USB cables and in that process I purchased two products from Mad Scientist Audio. One was their Black Magic and the other was the Ultra version. Both were purchased used from different sellers. I own two systems and decided to keep both. In both systems I use a AMR DP-777SE dac. In the system using the standard Black Magic USB the system was not using the built in volume control. About 2 month after purchasing the cable I tried using the internal volume control in the dac and it only worked at full volume. Thinking the dac was faulty I sent it back to TMR (great company) for evaluation. They tested it for 2 weeks in every configuration possible and determined it was working as it should. When i got the unit back (after a cost of approx. $200) I determined that the problem was the Black Magic USB cable. I contacted Bob at Mad Scientist Audio by email multiple times and he replied that his cable is incompatible with 1 in 50 produces and mine must be the 1. I then tried it in two other systems and also had the same results. Either the volume control didn't work or  I would get cracking noises. after many emails back and forth Bob would not exchange the cable for a working one and only offered to sell me a Ultra cable at a discount. I don't know what his profit margin or warranty policy is but I have never experienced this especially with a cable manufacture, I offered to send it back to him so that he could access the problem but in the end his last email read "Therefore I don't think it's worth you wasting anymore money trying to fix or exchange your cable." Very disappointing. The cable is now in the trash. I know that this is a small boutique manufacture but with the controversy regarding cable costs and  if expensive cable are necessary I thought that buy telling my story maybe it would alleviate this situation with this company.