KPIs are used to monitor supplier's performance. They can be qualitative or quantitative. Of course, service providers can be monitored by quantitative KPIs regarding the outcome achieved (such as uptime in IT contracts), timeliness of deliveries (such as in construction contracts)...
Reference: CIPS study guide page 117-122
LO 2, AC 2.2

Consideration refers to the exchange of something of value between the contracting parties and is a fundamental requirement for a valid contract. It can be in the form of goods, services, money, or a promise.
Without consideration, there is no enforceable contract even if other elements like offer and acceptance are present.
Reference:CIPS L4M3 Commercial Contracting Study Guide, Chapter 1, Section 1.1.1 - Essential elements of a valid contract.

Liquidated damages are a pre-agreed amount stated in the contract, payable upon a specific breach. These clauses are enforceable if the amount is a genuine pre-estimate of loss and not punitive. In this case, the £5 per tyre is a typical liquidated damages clause as it quantifies the penalty for non-compliance.
Reference:CIPS L4M3 Commercial Contracting Study Guide, Chapter 3, Section 3.2.1 - Liquidated damages, indemnities, and breach clauses.

Based on two famous precedents, Fisher v. Bell (1961) and Pharmaceutical Society of Great Britain v. Boots Cash Chemists (1953), the display on shop window is considered as an invitation to treat. The shop owner can change the price when his customer asks to buy.
Reference: CIPS study guide page 29
LO 1, AC 1.2

Call-off or blanket orders are common procurement tools used to streamline the acquisition of routine, low- value items. This reduces the administrative workload and simplifies the process, allowing multiple deliveries under a single contract, thereby increasing efficiency and control.
Reference:CIPS L4M3 Commercial Contracting Study Guide, Chapter 4, Section 4.1.2 - Use of call-off and framework agreements.