I've never had a problem returning defective items to Amazon. I've returned a $700 graphics card and all I had to do was drop the old one off at the UPS store. The biggest thing is you have to check if it's sold and shipped by Amazon. If it's sold by a third party then it's covered under a different return policy.
As to returning something because of buyers remorse or changed mind I've never done that so I can't say. I will always tell someone if you're not sure you'll like it then buy from Apple because they will accept returns pretty much no questions asked. Of course you pay extra for that service over Amazon or B&H because returns cost money but it can be a nice option. In the USA Walmart is the closest thing you will get to a no questions asked return but I think it's limited to twice or three times a year. The one near me will carry the iPad Pro but it's usually the base configuration.
Both my iPads were shipped & sold by Amazon.com/Amazon.com.
I suppose my frustration is that I thought it would be a quick return because I never even opened the shrinkwrap. I'm hoping to wait it out, but keep track to make sure I got the refund.