If you gotten a free design from me or traded to you or sold to you. It's all yours to do whatever want with it. You're not obligated to credit me but it would be appreciated and courtesy for the artwork if I made any. You can resell/trade/give away whatever ya want with it. You can do whatever you want with it cause it's legally yours and not mine anymore. So have fun! Don't feel guilty.

Growing up, it was confusing but gaining experience and doing physical research in businesses. When a video game or movie company commission a musician for music, the movie/video game company owns all right to the music unless the MUSICIAN sells them a license instead with a binding contract. Disney World has a section of the park with the floating mountains from the movie Avatar, they had to get a license from the company for it. Though since Disney just bought the company, they now OWN all the IP, movies, products, etc, so Disney don't need permission or buy a license cause they bought the company. So how it works?

But when it comes to Artist...artist believe it's not the same. Yes it is, it's a legal stand point and legally individual with the design given for free or trade or adopt, they own the right to it unless you sell them a license. A TOS isn't a license, it's courtesy agreement and should follow respectfully but the individual doesn't have to obide by it. Why? Well if there a situation where it leads to a court and Judge ask you what the person did, explain to the judge that broke the TOS. Judge would ask the person if they signed a document agreeing to any terms and person says no cause it was just written TOS anyone can read and nothing to sign. Judge is going to dismiss the case because the person didn't sign anything so not obligated. Judge would likely recommend speaking to a lawyer or legal representative about creating and making a license can sell.

So if I have a license, I have an adopt, I would sell the license. It's basically a contract in a way. If you really want to find more about License, contact a Lawyer specialize in copyright/selling.