Let's say, you're doing a commission for a client. They don't like the first sketch and decide to go with a different theme/pose , so you redo it from scratch and they like the second. You finish the commission, and they upload both the commission and the rejected one.
I honestly don't know what's right and what's wrong in those situations. Does the sketch belong to them even though it's not what they went with? Is it the artist's property and therefore they're not allowed to post it? Can you reuse the sketch as long as the character looks different after? Did they pretty much get a free sketch out of it since they asked for a whole new pose/theme?