An Offer Must Be Distinguished From An Invitation To Treat

It is important to know which party makes the offer and which party accepts it. In the case of goods on display in a shop, it has been decided that it is the customer who makes the offer to purchase and the shopkeeper who accepts it.

The price displayed on goods is not the offer, it is only an invitation for the customer to make an offer and the amount shown is an indication of an acceptable price. Consider self-service shops. Goods were individually priced; the customer took them off the shelf and placed them in a basket.