If shopping online then delete the cookie files. Do not log into say amazon or walmart so they do not know who you are.
They want your account as they say to give you a better deal but they will raise prices on you because they know where you live, the home and car value etc.
Unfortunately they can know the computer because it has a mac address number. You can change it with software but that is not known by 99.9% of the people.
Not sure about Amazon...as a Prime member, the pricing seems to be better when I am logged in vs logged out...