I personally think there's a difference though between say ordering an item of clothing with the intention of wearing it for one night then returning it, or buying a toolkit to use for a one off, and buying items that you exchange several times due to "faults".
I've never bought anything with no intention of keeping it, however as I'm really anal and ocd, the tiniest fault I spot makes me return it for another, faults that the average person wouldn't notice or even consider a problem.
For example when Amazon were doing 50 series Panasonic plasmas, I returned a few due to not being able to tolerate either the buzzing or vertical banding, so I exchanged a few in the hope of getting a "perfect" panel.
I personally don't see anything wrong with that, and certainly wouldn't put those scenarios in the same basket as people who buy things with ZERO intention of keeping it. Or using John Lewis 90 days returns as some sort of rental service.
Why I choose Amazon over other retailers is because their system is good, not to abuse. For example if I bought a monitor from **** and it had backlight bleed, I'd have a nightmare returning it, as they'd need it back first at my own cost, then they would test it and determine if they classed it as a fault, when people have different levels of tolerance of what is acceptable backlight bleed, and if they didn't class it as a fault they'd charge me a fee to return it, for testing etc. Plus the whole process with them could take weeks.
Amazon on the other hand will send me out a replacement before they've received the original so I can compare which one is better and then return one.