Not only personalized 'artwork', but I have seen a few Inspires for sale where the owner took a sharpie and wrote his FAA number on the top. Not very neatly either!! Then in his listing, he says he can transfer that number to you! Guess that's the lie he was telling to prospective buyers since he can't get the number off. Also seen people number their batteries with a sharpie.
I used a label machine to print my FAA number and put it on the batteries, so it is inside the bird. No alterations to the outward appearance.
I have re-sold all of my stepping stones, some at a profit, due to taking good care and posting GOOD pictures when I list for sale. It amazes me that some things sell at all on eBay due to lousy pictures. Dark, out of focus, upside down, in need of cropping, etc.