I already added it, but I thought it might require a highlight as well.
I see people (re-)selling characters and then charging for art they commissioned of the character while they owned it. I guess they're trying to get their money back, or even turn a profit? However, legally, with freelance work you have to negotiate and pay for rights to freelance work, such as commissioned artwork. These rights include the rights to repost, edit, sell and transfer those rights to a third party.
While I'm usually lenient on the redistribution and editing of commissions by the original buyer of the commission, within reason, I do not extend those privileges to anyone but the original buyer. And unless they have asked and paid for the aforementioned rights, they cannot sell the rights to my work and the character's new owner cannot use my artwork for anything.
In plain English, if any of the characters featured in commissions drawn by me changes owners, the old owners may not give away/trade/sell my artwork, nor may a new owner make claims to the artwork.
P.S. The same goes for gifts and trades drawn by me, of course.