in an advertisement if final willingness

Hi,

Most forms of advertisements are not actually offers but invitations to offer. An invitation to offer is an act done before an offer, in which one person induces another person to make an offer to him, it is known as invitation to offer. When appropriately responded by the other party, an invitation to offer results in an offer. 

A person can accept an offer through their actions. If you see an advertisement promising cash in exchange for used college textbooks, you could accept the offer by sending in your books to the person who published the advertisement.

Many offers, however, specify exactly how acceptance is to take place. For instance, the advertisement described above could state that you can only receive money for your used textbooks if you first register with the company. In this circumstance, simply sending in your books would not count as acceptance.

I hope this answers your question.

Have a good day.