I'm an illustrator, but not the technical variety so no good to you. You could try an artist's agents that have a range of technical illustrators on their books. you might pay a little more but you'd get a competent job. Most of these artists on the odd job cheapo websites are cheap for a reason and it looks like you've already experienced their level of professionalism. I suggest a Google of artist agents or a peruse of the artists and writers yearbook. Sadly my agent doesn't cover technical illustrators our I'd suggest them. Good luck!