Well I mean, this was a YCH. The buyer had no problem with the anatomy I'm sure because they saw the sketch prior to buying, so maybe ease up on the criticism.

Also it's clearly a rabbit. You're being rude.
If you have nothing nice to say about it, maybe don't comment.

Well the hand was just as big in the sketch for the YCH, so the fact that they bought it anyway and then had the gall to send their friend to complain about it doesn't make them look very respectable. You can paint your rudeness as constructive all you want, that's fine, but in my opinion, calling their drawing a "koala with big ears" is not constructive. It's just rude. Maybe next time your friend should make sure they're 100% happy with the YCH sketch before buying, and if they have an issue with a commission, they should speak to the artist themselves, privately. I'm saying this as an artist who does commission work and as the buyer of their other YCH. You decided to leave your rude comment publicly, so I felt it was only fair to call you out publicly.

Take care.