I prefer to pay 120 with free shipping than 100 + 15 for shipping. Not just me: most people. This has been tested repeatedly. Yet, it seems so irrational that r

I prefer to pay 120 with free shipping than 100 + 15 for shipping. Not just me: most people. This has been tested repeatedly. Yet, it seems so irrational that retailers don't believe it. But it's true!! And Amazon wins because of this.