Fun fact ad 3 - in some countries (Poland) there is a concept in law of a public promise. If a corporation publicly promises something (a competition usually), they are obliged to act upon it, even if there were no signatures on the other side.
Which may seem to apply, but this was an offer to add a guarantee to the terms. Whereas merely advertising a price is just an invitation for the buyer to make you an offer. Here is an almost as famous case.
https://en.m.wikipedia.org/wiki/Pharmaceutical_Society_of_GB...
I am not surprised our fellow common law jurisdictions like the US reached the same conclusion.
The case law that makes up English civil law, especially the early stuff is really fascinating stuff to me. IANAL but understanding the contact law from these cases has won me several disputes in my professional life.