I only have one really ongoing regret about selling a bead I loved and totally thought was one of the most beautiful things I'd ever seen as far a color, wear, and condition. I've briefly mentioned this before.
A collector business "friend" from TN would come to NC now and then, looking for beads to add to his collection, and in a moment of total weakness I sold him a lovely ~ 3" long, thin, twisted Nueva Cadiz bead with a white stripe down it. The thing was beautiful and perfect. I made him promise me that he would give me first right of refusal if he ever decided to sell it, and he agreed. Later he does sell it telling me apologetically that it was the highlight of his Nueva Cadiz collection, and he sold the whole collection to one "collector". If you bought "my" bead (lol) from J.D. in TN years back please be good to it! Sigh.
Conclusion, for me, much worse to sell something you love. Though sometimes you "have to". You also have to know it's never coming back- unless you are very lucky somehow.