By the same token, AT&Ts malicious pricing malware running in your browser could be construed of "unauthorized access" of your own computer, thus AT&T would be violating CFAA.
But don't sit there and pretend that you can say, "well, they let me do it because some of the code ran client side." No, that's not how it works. Changing the price of a $100 service to $10 on a website, is like taking a bar code from a $10 product and slapping it on $100 product. The biggest difference is, since it involves computers, there are even more crimes committed.
In none of these cases are the companies condoning or supporting your actions. You can try the argument that the bank teller gave you the money and that it's bank policy to do so. But it probably won't work.
It's strange to see people bending over backwards to deny that this is a crime. Surely if someone manipulated your bank's computers to wire transfer your entire balance to another account, you wouldn't be asking, "what crime could [they] have committed?" You'd feel like somebody stole from you.
Using your store analogy it would be like bringing a television to the cashier and telling them you will pay $10 and they accept.
I doubt a “reasonable” person would think of it like the latter case, but for people who think about software agents, it’s interesting to think about.
Disclaimer: don’t try this at home…
Just because you can physically enter a strangers house does not shield you from trespassing charges.
Society / the legal system is not code. There is all sorts of nuance and morals and subjectivity involved beyond the "bits on the wire", so to speak. You can go to prison for accessing a website you know you shouldn't, even if the HTTP response code is 200.
This is why educating the public about jury nullification is so important.
The server validated that the coupon code was legitimate, but the actual discount value of the coupon code was validated client side in JS for some reason.
So he could turn any 10% off coupon into a 100% off coupon by modifying the API requests during the checkout flow. I'm sure this was illegal but he ate a lot of free fast food before they ever fixed it.