When I first started PS Audio some 40 years ago, times were tough. The company was definitely a labor of love, one we not only didn't make any money at, but instead, invested every nickel we had (and didn't have) just to keep the dream alive.
One of my regrets was selling my album collection. Over my many years as a DJ I had amassed a pretty amazing record collection. Thousands of first pressings, hard to find albums from all over the world. One by one to pay the bills, I sat at the swap meet each Sunday selling enough of them for one to two dollars apiece to buy groceries for the week. The good news is that money carried us through some tough times. The bad news is obvious.
These sales took place in the 1970s, a time when there was no Napster, no worries by labels of copying and owner's rights to purchased music. That's not so true today.
Selling your own copies of that same music comes with some risk if you were not the original owner. In my case, many of the albums I sold were promo copies and gifts from musicians. Technically, I broke the law selling them. The same would be true today if it was a CD, not originally purchased by me.
This whole copyright thing makes my head hurt and to be honest, I treat it as I do the warnings on bedding I purchase not to remove the safety label.
Of course copying and selling is wrong, and wrong on any number of grounds. But what you do with your media collection, regardless of how it was obtained, is your business.
That's not legal advice. It's just my opinion.