I posted my Karl Theme when prices were still about 16/19$ for each theme (only a few themes were priced 20$).
It started selling good, until a couple of weeks passed and the prices were raised to 30$.
I think the header looks very amazing
But yeah, as stated above, the typography is the major problem. Reading is a bit of a pain, the text is too small and too thin. While minimalistic themes are very popular among tumblr users, premium themes should offer a bit more. Pick a solid typeface and a nice color palette (even if it’s greyscale), add some contrast.
White space and line height are important, they affect the readability of sentences.
There are some problems with disqus as well http://summernightsdemo.tumblr.com/post/84585728352/grease-summer-nights#.U6LmN7GMJ4o
Here is my theme: http://themeforest.net/item/kaye-business-tumblr-blog/7372153
This is great , guys!
Though I wish I waited a couple of days before submitting my theme (approved just this morning)
Going to work on new themes <3 Good luck, everyone!