You could respond with the a comment inspired by the no extra payment for the artwork or similar, I probably would but then I am not particularly bothered about feedback.

Only ever received any once, from the same person, and I was not hurt but extremely annoyed not by the feedback but by the fact she tried to scam me. I was almost disappointed when they were removed as I really enjoyed composing the followups.

I would email them saying you are very sorry but had you not included the biro markings the item would have definitely been not as described and you would have been more than happy to refund if it had been returned.

Keep trying with ebay, where one person won't help another might.