While the fault of what happened is on both the Artist and the Commissioner, I would say more-so the artist.
The Artist only ever provided a finished piece the Commissioner mistook for a work-in-progress, where no W.I.P had been provided, just a finished product with missing details (Mostly the character on the right. Their Tail was white, the mouths on the tail look borderline unfinished and rushed, and the character is missing its ear piercings and collar.)
Even when the piece was corrected the only thing that seems to of changed was giving the goo-girl character more goop and changing the tail of the other character to purple, then had the audacity to say the commissioner would need to pay "Editing Fees" if they wanted anything else changed...while the artist themselves had still missed some details. This comes off as scummy on part of the artist, not to mention making this artist-beware seem petty and even vindictive. As for the nudity the Commissioner expected the YCH shows none of the example characters in clothing, nor are examples provided to show otherwise.
The Commissioner should of asked before hand for examples when none were provided however, they should of been told exactly what they were getting before spending money. I do not think it is their fault the artist seemingly rushed through their work and expected them to be happy with whatever they got. If I went to get something made, provided examples, and got a rush job with no showings of a work-in-progress, I would be asking any service for a refund.