WordPress Licensing Question…..

Hi, I build websites for mortgage companies and have recently been looking to implement a CMS to enable my clients to publish their own blogs and make changes to their site without editing html…. I like wordpress, it looks like it is just what we are looking for, but I’m wondering if there are any licensing / rights issues with us selling our website when it is part of a wordpress implementation…… I’m not up to speed on how open source plays out in this scenario…

Any feedback greatly appreciated, I want to make sure there are no issues before we move forward…. thanks!