Slackermedia promotes free and open source software, with the notable exception of Lightworks (without which there would realistically be only one professional-level video editor: Kdenlive). That doesn't mean that free and open source software is all you can use on Linux. There are several off-the-shelf products that you can purchase and use:
These applications have been tested by Slackermedia and are known to work on Slackware, but this page is for reference only. Slackermedia offers no unpaid support on these applications.