Since they are both under the pretence of paying someone to create something for you I think it's a worthy comparison. I've seen people receive fursuit heads and on arrival it had with bad stitching, or wrongly shaved fur, and they would be told they can fix the issue themselves. If an artist forgets to a clothing item or fur marking, doesn't that go under the same definition?
The art in question is for a personal dakimakura, so it would be printed and looked at a lot by myself. It's purely a precaution as I would hate to print it and notice something that flew under the radar. Maybe it's a bit much but It would bug me.
The problem is many artists in their terms of service refuse changes after a certain point. To fully respect those terms and still be satisfied, if they made a mistake, the only way would be to edit it myself. I could just accept the art I see as incorrect but isn't that kind of wrong? I paid for a service why should I just grin and take it if it can be changed and nobody is being harmed in the process? Their reputation isn't soiled as no one else would see the edit, and they would never actually know it happened.
Even then the original question was about the ethics of sharing PSD files, not the moral obligations of my personal reasoning for wanting it. I don't see why that is being scrutinised.