Amazon is high volume, and they can afford to cut prices by not having a brick and mortar stores. Plus their logistics (delivery network) are unmatched. All of this means they can pretty much undercut most the competition on price (and therefore attract higher sales volume), and still make enough profit to be successful.
The purchase is direct from Amazon, correct (and not a 3rd party vendor that sells on Amazon as a portal)? If its the same listing I am looking at, it is. Amazon is really reliable. But mistakes just get made once in a while.
Merchandise returns are extremely easy on Amazon, in the event you end up having to do one. They give you a UPS label to print out, just slap it on the box it shipped in and seal the box, and take it to a UPS store (or you can probably call for UPS pickup). Since it was their mistake, they pay for shipping. When they made a mistake for something my wife ordered, they made it right by shipping the replacement overnight at no cost. Even when its a mistake I made (ordered some electrical part that were the wrong color) the return shipping was only about $2.