Amazon is the one that advertizes the price. Once it's advertised and a transaction has been completed, that's a contract. That contract includes the possibility of returns because they compete in the retail space, where there is an asymmetry in that the company has had ample opportunity to evaluate the product and price it accordingly, but the customer doesn't otherwise have much to evaluate on. If Amazon does this at such an astronomical scale that they don't notice a big price discrepancy, that's the cost of operating such an astronomical scale. They still made the contract - and it was even their lawyers who wrote the contract and spend hours poring over it. If I order truck loads of landscaping material to be delivered to my house and I later learn that it wasn't such a great price, you better believe I'm now stuck with that material and the bill.
I actually had a similar event happen in a real-world retail store. They were advertising frozen chickens for an absurdly low price. I checked with an employee that the price listed was not a mistake - they said it was correct. I grabbed a manager, and checked that the price listed was not a mistake - they said it was correct. I took 2 cart loads of frozen chickens to the front of the store - and they didn't notice the price was absurdly low until I had already swiped my credit card and the cashier was telling me the total. By the time she grabbed a manager, the transaction was complete, and the same manager who confirmed the price now told me it was a mistake. Fuck them - they listed the price, I checked, I finalized the transaction.
At first, I thought you were talking about the general social or implied contract between a retailer and consumer, in the general sense. But if you're talking about the explicitly written contract that the lawyers wrote, which is the Conditions of Use, then the allowance for pricing mistakes is right there in the "Pricing" section of the contract, including a description of what happens in such events:
> With respect to items sold by Amazon, we cannot confirm the price of an item until you order. Despite our best efforts, a small number of the items in our catalog may be mispriced. If the correct price of an item sold by Amazon is higher than our stated price, we will, at our discretion, either contact you for instructions before shipping or cancel your order and notify you of such cancellation. Other merchants may follow different policies in the event of a mispriced item.
 edit: and I'll admit I hadn't actually read the contract myself. I do when (a) I think there's actually a reasonable chance I'll walk away from the transaction rather than just risk losing $15 because I'm not satisfied, and (b) when the company bears some cost due to the complexity of the contract - like when they're standing there waiting for me to say I've read and understood it. I think it's problematic that almost no one reads what they're agreeing to, and everyone knows that, and we're all just okay with it. No idea how we fix that, but so long as we're talking about asymmetries in these transactions, the effort companies put into these contracts that they know perfectly well almost no one is reading scares me more than handling of price discrepancies.
After a cartload at one store; went to another - same. It was system-wide. So I went to a couple more over the next couple of days (I had a large chest freezer at the time).
Finally, about the third day in the discrepancy was noticed and the signs/system changed.
Best "mistake deal" I've gotten so far - but nothing like this camera deal at Amazon.