* Slow to ship if non-Prime member
https://www.forbes.com/sites/kateashford/2016/01/30/amazon-shipping/#4297cbb86517 Noticed recently my non-Prime Amazon fulfilled shipments taking more than a week to get out of Amazon's door.
* Want express shipping or 'free' 2-day shipping for Prime members which for Prime pay $99 annually for that privilege. Amazon does not always use reliable UPS, USPS, Fedex, or DHL, but instead sometimes uses unreliable BBB F rated Lasership headquartered in Fairfax County Tysons area
http://nymag.com/selectall/2017/09/lasership-amazons-shipping-partner-is-a-problem.html sharing the horror stories and why Amazon continues to use them.
* Not always lowest prices - time.com/money/4010101/amazon-lowest-prices/
* If you care about your fellow human beings, inhuman treatment of warehouse workers to point of death -
http://highline.huffingtonpost.com/articles/en/life-and-death-amazon-temp/
If the choice is available using Amazon and the price difference is not much higher, though at times it is lower than Amazon fulfilled, I use Amazon 3rd party sellers who do NOT use Amazon for order fulfillment (this is cleared labeled if they do) with at least minimum 90% (through strive for 95%+) seller ratings, who even over the last year, gets my non-express shipments out the door within a couple or a few days if that, and knowing they are not abusing their workers like Amazonions in the warehouses, and they use reliable shipping methods, not Lasershit as some call it.