Unilateral interference or intervention by a small number of States raises the question of the competence and democratic legitimacy of the action, even if it is based on an international treaty of the States concerned and between the States concerned. A unilateral treaty is different from a bilateral treaty in which the parties exchange reciprocal promises. Bilateral contracts are often used in commercial transactions; a sale of goods is a kind of bilateral contract. As a general rule, if the offer results in a unilateral contract, the offer cannot be revoked once the bidder has begun to execute it. The formation of a unilateral contract can be proven in the English case of Carlill v Carbolic Smoke Ball Co.  In order to ensure the effectiveness of the Smoke Ball, the company offered a 100-pound reward for anyone who used the product and contracted the flu. As soon as she became aware of the offer, Carlill accepted the offer when she purchased the Smoke Ball remedy and completed the prescribed course. After the flu, she was eligible for the award. Therefore, the company`s offer to pay 100 pounds sterling “in exchange” for the use of the Smoke Ball-remedial and to guarantee that the flu will not be taken into possession, was made by Carlill. An invitation to treatment is not an offer, but an indication of a person`s willingness to negotiate a contract.
It`s a pre-offer communication. In the UK, Harvey v. Facey is an indication to the owner of the property that he or she might, for example, be interested in a sale at a specified price, was considered an invitation to treatment. Similarly, in the English case Gibson v. Manchester City Council, the words “may be ready to sell” were considered a price notice and therefore not a separate offer, although in another case involving the same policy change (Manchester City Council experienced a political change and stopped the sale of council houses to their tenants) Storer v. Manchester City Council “ the Tribunal found that an agreement had been the signing and restitution of the sale contract by the tenant, because the language of the agreement was sufficiently explicit and the signing on behalf of the Council was a mere formality to be fulfilled.