Law question, please help!

If good are displayed on the shelves of a department store or supermarket, the store is not offering to sell the goods; it is merely inviting its customers to make an offer to buy them. When the customer takes the goods he has selected to the cash desk, he is offering to but them.

Pharmaceutical Society of Great Britain V Boots Cash Chemists (Southern) Ltd (1953)

所以，間shop擺出黎只係advertisement，就算係話寫錯價錢都冇問題，冇得話佢。但係之後owner講HK$10,000.00就係一個offer勒。而Natalie (N)冇即時accept個offer，所以個contract仲未成立。但係N有 ask for 3 days，所以3days之內如果佢accept都係可以既。Owner其實唔可以隨意賣俾其他人。

An offer may specify that his offer is open for a certain period of time. In the case of Dickinson V Dodds (1876) an offer to sell the property (1st OFFER); an offer to keep the first offer for a period of time (2ND offer).

除非N提出咗其他offer (2nd offer)或owner withdrawing 咗呢個offer before N accept。(Once an offer has been made, the offeror - that is, the person making the offer - may change his mind and decide to withdraw his offer. This process is called revocation of an offer.

No, Natalie has no reason to take action against the shop owner. The marked price is only an invitation to treat and not an offer!

So, the owner can decide whether to sell the necklace to Natalie or not. Even the shop owner has change the makred price for Natalie, The reasonale is still the same.