There are several instances of conflict in a marketplace. Over time the law of contract was established to lay down a set of rules for all parties to a business transaction.
A contract is a legally binding agreement between two or more parties and if necessary the parties may resort to the courts to decide.
A contract needs to have a range of elements present and reaching agreement is the initial step.
Agreement = Offer + Acceptance
An Offer is a proposal to give or to do something and when accepted there is said to be agreement. e..g. A bid on a house at an auction.
It must be clear and may be implied by conduct e.g. taking goods to the checkout.
Acceptance is a positive unqualified assent to all terms of the offer e.g. The vendor is happy to sell the house.
Exception:
Goods on display are merely an invitation to the buyer to make an offer to buy but are not necessarily an offer to sell. This concept is called “Invitation to treat”
In the event of the seller refusing the offer to buy then we do not have acceptance or agreement
A potential contract would fall at the first hurdle if agreement is not reached.
Note
Very specific answer needed