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!
Amazon doesn’t track users, but it does have various sellers selling the same items. The search results aren’t always in the same order and sometimes the price on the item page is based on whichever seller has that item.
For example, I wanted a faux leather jacket. I found dozens of them in various sizes from different sellers. Changing the size on one page changed the seller entirely.