I built and sold shortwave transmitters when I was in elementary school (1960s). One of the kids got buyer's remorse and wanted his money back. I told him I couldn't (had already spent it

).
Next day I come to school and get called to the principal's office. I go in there and in the corner of my eye see the kid and his parent. I figured I was in deep trouble.
Principal looked at me and asked, "you know it is against the school rules to sell stuff at school, yes?" I said "yes" while getting ready for serious beating. The principal puts the transmitter I had sold the kid and said, "this is darn cool!" Asked me to give the money back to the kid and that was that.
How is this for noteworthy?
I managed the development of professional audio equipment for broadcast and post production fields (and a workstation with audio subsystem while at Sony). Two of those products won technical Emmy awards for excellence.
My team won a third one while at Microsoft, this time for the modern version which is to stream audio/video on the web:
http://bryan-brown.com/emmy07tech/portraits/pages/2210_0075.htm
So no, I don't design commercial audio equipment. I think it is the absolute worst thing one can do: turning a good hobby into a bad business.