在superｍａｒｋｅｔ買東西

係你比offer佢.
超市標價出售貨品, 並非offer, 而是Invitation to treat. 顧客拿貨品到收銀處是向超市作出offer, 所以超市可以不接受你的offer, 拒絕賣貨品給你.
商店標價出售貨物=Invitation to treat 這原則在Pharmaceutical Society v Boots Cash Chemists (Southern) Ltd. 及Fisher v Bell 這兩個案例中已清楚確立.
兩個案例的內容可參考:
Pharmaceutical Society v Boots Cash Chemists (Southern) : http://en.wikipedia.org/wiki/Pharmaceutical_Society_of_Great_Britain_v._Boots_Cash_Chemists_(Southern)_Ltd.
Fisher v Bell : http://en.wikipedia.org/wiki/Fisher_v._Bell

Supermarket將貨物陳列在架上, 並標明價錢, 係佢Offer將果件貨品以某個價錢(Consideration)賣俾你. 你將貨品從架上拿下, 放到手推車內, 係你嘅Intention to Accept.到此, 你同Supermarket重未有Contract. 所以你可隨時放低貨物唔買. 到你將果件貨品拿到Checkout, 放在Checkout 帶上, 而職員將貨物價錢入機, 咁就係你Accept Supermarket嘅Offer. 有左Binding Contract. 你而家話唔買, 技術上Supermarket可以控告你違約(Breach of Contract). 到你付款, 你就係支付左個Consideration, 咁張Contract就execute左嘞.