Agreed. It is extremely childish for people to come to YOUR page and proceed to complain how you are over charging for your hard work. It is uncalled for, and just plain rude. If they understood the work you put into your art, they wouldn't be saying things like that. But regardless, your work is great, and I wish you only the best. Hopefully you will get some good money for this work, as you deserve it.
I kind of figured the line art wasn't markers, since they could easily blend and start to blur when applying all the marker colors. I was just curious. They are so bold, I love how they look.