1. No, you don't need to know html to use the theme.
2. It really depends on what sort of changes you want to make?
Here is an excerpt from the ClassiPress FAQ page which probably applies to you..
Q: I love ClassiPress but want to change the design around to better fit my site. How can I do this?
A: If you are familiar with WordPress theme files, css, and html then you should have no problem customizing ClassiPress to match your existing website. This is not covered under the ClassiPress support package so it will be up to the community to answer your questions. For starters, you’ll want to edit the header.php and style.css files. If you aren’t technical then I’d recommend hiring a WordPress consultant.
3. No. Since this is digital media there are no refunds once your purchase has been made.
If you are not already familiar with WordPress and how to updates themes, then I would recommend that you install WordPress first and have a look at how it all works before you jump in and purchase the ClassiPress theme. This will help you have a better understanding of how you go about turning your WordPress site into a Classifieds website using ClassiPress and should make you feel more comfortable about your purchase :)
Originally Posted by nobreak
