Oh, and yes... he said he uses the mat all the time (showed it to me, I never saw one before) and puts green ink on the edges of CDs he really likes.
My gut said it was a premier waste of time, but I don't have the technical insight to back that up.
The Alesis is equipped with a hard disc.
Your gut seems more reliable than some people's guts. The guy has bought into some nonsense. Many people do buy into nonsense, in audio and in other aspects of their lives. Most people can't tell good reasoning from a hole in the ground.
If you think about how a CD works, you will realize that spinning it first, and exposing it to magnetism, are irrelevant to what the laser will read off of the disc, and consequently, it cannot improve the sound. I think people should study these things, in a broad and general way, so that they are less likely to be suckered. Here is a link to how CDs work:
http://www.howstuffworks.com/cd.htm
That article probably has as much depth as most people need. But knowing that little can help one avoid being a sucker to some of the more extravagant BS (assuming one has the ability to reason logically; if one does not, then no specific knowledge is going to guarantee that one will not be a sucker). For example, since the laser (i.e., a focused beam of light) is not shined on the edge of the CD, logically, it makes no difference whatsoever what color the edge is, and the green ink idea can therefore be known to be pure BS.
And, "opportunist" or not, you are correct, if he is selling his collection anyway, at a price he set, when he is not desperate for money, it may as well be you who buys from him as anyone else. I don't think there is anything wrong with what you have done, assuming you have accurately related the story. I don't think there would be anything wrong with you buying discs that you did not want to keep, and only purchased them to resell at a profit. He decided to sell, at that price. I believe, however, that what he is doing is probably illegal, as backup copies of copyrighted material are only legal when one retains the original*.
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*I am not a lawyer, and laws vary from one jurisdiction to another. Consequently, nothing I state here or anywhere else should be construed as legal advice. For legal advice, one should consult a relevant expert within one's jurisdiction.