Two things going on here: 1. First, I'm a bit baffled by some of the responses along the lines of "Amazon should just own their mistake". Sorry, but in the real world, "finders keepers" rarely applies (unless you're talking about crypto, but I digress...). I would certainly want a bug corrected if it were in my favor, and if a bug went the other way, I might need to re-evaluate my company satisfaction based on my new…
If Bob signs a contract for Alice to paint a fence for $800 and a copy-paste error transfers her $1000 instead, yes.
But if the copy-paste error happened before the contract was signed? Leading to Bob promising Alice $1000 and signing a contract promising it? Then in all probability, Bob will end up paying the contract amount.