I have stopped using amazon ever since they openly admitted to changing prices based on what they thought your income was. So for instance, if you did searches for medical books or law books, they assumed you were a wealthy doctor or lawyer and thus every item you looked up after that had the price cranked up.

heres the proof:

http://www.cnn.com/2005/LAW/06/24/ramasastry.websi te.prices/