So there are some issues, some small, some very big.
This is a big issue, and actually implies to me that you did not design this yourself, which is bad news for a theme designer ...
Definitely needs to be spacing between these buttons. When I click "Go Shopping", I'm brought to a "No Permissions" page ... do I have to be logged in to shop or something?
Also, clicking Request a Custom Theme gives me this:
Really not professional. If I make a thread here, will only you and I be able to see it, or others as well? As a potential client I have no idea, and making that request via a typical forum layout makes me uncomfortable. You should at least use xThreads to customize some kind of content form if you insist on using MyBB to receive the request.
You have tooltips
everywhere -- which is obnoxious enough -- but sometimes the tooltip is a repeat of the text I am already hovering, which makes this a 100% useless detail. (Also, hovering over the Home icon here causes some pretty wonky animation.)
These aren't all of the issues, I am sure. I was able to discover these in a cursory examination, so if I kept digging I am sure I could find more. There's also the fact that the forum just doesn't look that great or polished IMO, which is problematic when you are selling themes.
Hope some of this is useful for you.