I must admit that I have done this.
Before I left, my main character was Kamaria.
Now of course, I use Turtle often. I got rid of (well, didn't use, I still have her since she's in a pack) Kamaria since I just didn't find her appealing anymore. There's nothing about her that stuck out, and she just looks pretty goth.
As for selling/giving away characters, if I had a character that was used for a while, I wouldn't want to give it away. It's my character still, and I still care about it. I wouldn't want some random person to take my character and change up everything, not follow it's personality, etc.
I usually take characters after a while and sorta bring them back, sometimes with a changed personality or appearance, such as my wolf characters Cetta and Sala. Cetta was for a book I was making, but I ended up not knowing where to continue and have the book lead to and quit it. Sala was just a random drawing I made. But I've decided to bring them back a bit, redrawing them and putting them in different roleplays.
I usually abandon characters that I never used at all, but ones that I've spent a lot of time on I'll use for for a while. And some are lucky and will be used a lot after a while.