If a site has prices stored on the frontend and a user edits the price to make it lower, do you think the user has a legal basis to receive the item at their new specified price? I don't think many jurisdictions would say they do.
Further, in many places your example itself falls apart.
> If a site has prices stored on the frontend and a user edits the price to make it lower, do you think the user has a legal basis to receive the item at their new specified price?
There was a case like that in the early days of online shopping, which was actually decided in favor of the customer. The prices of items in the shopping cart were stored in form fields, and the customer edited them before placing the order. The court considered that a counter-offer which was accepted by the store. (It probably wouldn't go that way today; for one thing online stores have gotten smarter about trusting data from the client.)
That's a bit different from simply editing the client-side view and never informing the merchant about the change, of course.
Further, in many places your example itself falls apart.
https://smallbusiness.chron.com/company-advertising-price-wr... https://www.findlaw.com/smallbusiness/business-contracts-for...