My girl was looking for a dress for Halloween. Yesterday she found one on Amazon for € 35 and put it in the cart, but did not buy it. Today she looked it up again and it was € 50 so she asked me to look it up with my phone with my Amazon account - it turned out to be € 23 for me, less than half of what it’s for her!
My guess is that it’s something like camelcamelcamel which shows the prices over time in a graph? Here’s an example of a frog plushie https://camelcamelcamel.com/product/B09RN4YCXG?context=search&cpf=new-used
People should never trust Amazon or the “% off deal” that Amazon is advertising. Always verify against camelcamelcamel.com to ensure that the price is actually a deal and not artificially inflated due to some demand spike or their algorithm thinking that you really need it right now.