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
Motels and hotels have been doing this for decades. Check out room prices in college towns on game weekend.
I learned about supply and demand in middle school.