When you sell on multiple channels beyond Amazon – such as your own Shopify store, eBay, Walmart, or other platforms – you become fully responsible for tracking where you have sales tax nexus, calculating appropriate tax rates across 11,000+ jurisdictions, collecting sales tax at checkout, and remitting payments to each state on schedule.

You’ll need to monitor your nexus status across all channels combined and implement tax calculation software or manual processes for compliance on non-Amazon sales. Consider using automated sales tax solutions like Avalara or TaxJar to handle this complexity efficiently.