That’s a tiny part of the problem with Amazon.
Ever wondered how they always seem to have the stuff you want fulfilled by themselves and cheaper than anyone else?
The not smart retailers add their products to the Amazon platform. Amazon monitor their sales. If something takes off Amazon source it and supply it themselves, cheaper. Thus shafting the retailers they partner with.
For most retailers you work on an 80/20 split. 80% of your profit comes from 20% of your lines, the rest is put down to “market research”, as in, you try it, it doesn’t sell, so you blow it out at cost.
Amazon don’t have any loss leaders or dead lines because they don’t have to market test anything. Their retail partners do that for them, they then just pick up the good lines and run with them.
I regularly get clients ask me to add their product ranges to Amazon, I tell them the facts, most still do it though. Any retailer that partners with Amazon is feeding the beast that will kill them.
The big photo libraries do exactly the same thing to photographers. If they see a particular image or series of images is doing well they’ll have an in-house photographer on a salary reproduce the same shot then the original images are banished to page 300, allowing them to clean up. Again no trial & error or guesswork, just copy what works and make sure your own collection has prime position in the search results.