Mary Beth Westmoreland, Amazon’s VP of Worldwide Selling Partner Experience, speaks Tuesday morning at Amazon Accelerate at the Seattle Convention Center. (GeekWire Photo / Todd Bishop) Amazon is introducing tools to let independent sellers manage their sales on four of its biggest rivals — eBay, Shopify, TikTok and, yes, even Walmart — from Seller Central, the same dashboard they use to run their Amazon businesses. The multichannel selling tools, announced Thursday at Amazon’s Accelerate seller...