I can't see why some people get so upset about making profits.
If I pulled a keyboard out of a garbage can, cleaned it up, tested it, and sold it for $100, I would just say that I had a stroke of good fortune.
If I bought a keyboard for $50 and sold it for $100, that would be a lesser stroke of good fortune.
In my life, the opposite of those 2 scenarios are usually what has happened.
As I learned it, the definition of a "good business transaction" is where both parties walk away satisfied with the deal.
If I stumbled across a pile of valuable keyboards for free, or cheap, I would feel perfectly justified to sell them at the "fair market price" and if I offered a "good" or "great" deal to GHers on this forum, well, that would be a very kindly gesture, but I do not think that I would be an @sshole if I didn't.