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!
They do the same as the airlines, if they see you have interest they raise the ticket price
Edit: if you use a vpn and check airline price from another IP you will see different prices for same flight. And on Amazon my printer ink for obsolete model was $8, once I starred buying it started to hit $35-40.