You have a web site that sells trinkets and then you decide you want to expand your business but handing over those products to the behemoth e-commence site, Amazon. So you upload your products to the Amazon Marketplace and then all of a sudden, Amazon is outranking you for all your product queries. Surprise, surprise - what did you expect?
John Mueller from Google was asked about this question this morning on Twitter and responded with a poll on how you'd like Google to handle it. The question was "if we are uploading same product catalogue on Amazon/marketplaces and also on our own e-comm website, will this impact our ranking?" John Mueller's respond was kind of funny, because he spent the time creating a Twitter poll.
He said "What do you expect to happen in search? What would you expect as a user?" He offered these options (a) I love seeing double, (b) I prefer diverse answers or (c) I would like a cold beer.
What do you expect to happen in search? What would you expect as a user?
— John ☆.o(≧▽≦)o.☆ (@JohnMu) July 31, 2018
That is John saying - Google can only rank one web site in the first position.
Forum discussion at Twitter.