I went to my local dealer and tried to borrow cables to compare to my cables. I listened to some different models from a well known brand in the dealer's showroom. They had one pair of speaker cables and two power cords that they could lend me. They could not supply the other lengths because my main ICs are 5M, and they did not want to order them if I would not buy them first. So I got a flavor for the brand, but people kept telling me that I should really audition the entire suite for my system and the dealer could not provide the rest of the cables to try.
I then contacted a cable company directly and they invited me up for a factory tour. I met the designers, saw how the cables are made, met the assemblers, listened to music in their incredible research and development listening room, swapped some cables, listened some more and then spoke to a salesman. He made suggestions based on the gear I owned. I then gave him a list of the cables I needed and the required lengths. Two weeks later, I got a call and drove back to pick up an entire suite of cables custom calibrated to my specific equipment to audition at home for one month.
I left for vacation, left the system on for ten days of break in, came back and listened to them for an additional four weeks. They were so much better than what I had, and that other famous brand of speaker cables that I tried, that I bought the cables through their local representative. I bought the demo suite that had just been made for me, but the local dealer came to my house to ask questions, hear my system and complete the paper work. I could have just returned them, and there was no deposit, but I kept them and have been happy ever since.
I decided to buy the cables because of the incredible level of service, the trade in values of my old cables, and the sound quality of this particular model range.
I agree with those who have suggested that the only way to really know whether or not to buy cables is to listen to them in your own system. It sounds like DaveC encourages that as well. This past weekend I listed to two competing brands of power cords in a friend's system. They sounded very different from each other. He has one in for audition for three or four weeks. Listening over time is the best way. Perhaps one can narrow the list down by looking at specifications and talking to the designer.
I once met a designer who showed me seven graphs of square waves, the corners of which were highly magnified. It was incredible to see how the shapes at the corners of these sine waves varied between the seven popular cable brands. At regular magnification, they all looked the same, but once blown up, I think to 10-50 times but can't remember, the corners looked wildly different and the designer explained how the shapes corresponded to the different characteristics of a particular cable's sound. It was fascinating. My cable brand was not one of the seven. That would have been interesting to see.