Try to buy replacement printer ink for a HP 8600 printer. This is a super common machine sold on special in Costco and Best Buy, possibly the most popular general purpose printer out there.
Seriously, go to Amazon's site and try to just buy some replacement cartridges for it. The first result looks great, tons of reviews average almost five stars, appears to be sold by Amazon and made by HP: http://www.amazon.com/HP-Magenta-Original-Cartridges-CR314FN...
Now scroll down and look at the top customer reviews. Something is going on here. Are these real or refilled? Who exactly is selling them? OK go back to search results and look again. But there isn't any entry that stands out as obviously just made by HP and sold by Amazon, they all have similar problems.
Ugh. This of course happened to me the other day. I spent 10 minutes trying to just figure out how to buy real OEM printer ink, gave up, and navigated over to HP.com where aside from typing in all my info again, it was painless and next day shipping was free.
This has become a constant problem that Amazon has to fix.
The next exercise for the reader is to try to find a pair of genuine Apple OEM headphones, the kind that come with the iPhone, that can be bought with actual confidence. That should be the easiest online shopping task imaginable, but it's literally impossible at this point on Amazon. Not slightly frustrating, impossible.
And don't get me started on the switch to USPS shipping.
Despite their seeming chokehold on online shopping, Amazon is vulnerable to competition that can solve these kinds of problems.