As of February 24, 2015, some Marketplace items no longer provide support in the forums. Sellers have the option to provide support on their own site or via a 3rd party application.
Visit the Marketplace item's page and look under the "Support" tab. In addition, if you see the forum and are able to post a new thread, it's the correct way to request support.
Some sellers left their forum open in read-only mode to help answer FAQs and provide documentation here.
If you have any support questions, please contact the seller directly per their instructions on their Marketplace item's support tab. Thank you.
Support for the Taxable Marketplace plugin by dikiyforester.