Take their criticisms positively and don't get discouraged! Learn from those that have "been there done that" and move forward.
Things I would do:
1) Get your own domain and site hosting. Consolidate all designs into one site.
2) Continue you social marketing... don't let up!!!!
3) When developing your site first focus on usability. The user experience should be tops on your list. Are things easy to find and purchase? How many clicks to a conversion?... that kind of thing. Second should be the "look and feel" of the site (your brand). SOOOOO many people get these two backwards.
4) Do as GN suggested... find a site you think is killer, a leader in the space, and emulate it. There is much to be learned from your competitors.
4a) Make sure you are competitive. You prices seem on the high side for what you are offering.
5) Continue you social marketing... don't let up!!!!
6) Be prepared to wait it out. It can take well over a year to get any real love from Google or the other search engines. Organic clicks are earn.
6) Continue you social marketing... don't let up!!!!
7) Make your designs "look" more original. Make them appear to be unique. I know that's vague but it can be done. Use your (or someone else's) imagination
8) Continue you social marketing... don't let up!!!!
9) At this point you need to start testing the PPC waters. Please do your research here. The learning curve can be quite steep and expensive.
There are really so many other things you can do, and those will come to you over time, but it would be very difficult to cover them all in one post.
Good luck and don't give up!