Which of the following will help the bargaining strength of a buyer?

Detailed Explanation:

1 (Make in-house): The ability to produce in-house reduces dependency on suppliers, strengthening buyer power.

4 (High spend proportion): A high proportion of spend gives buyers leverage over suppliers who are reliant on their revenue.Limited suppliers (2) and high switching costs (3) reduce buyer bargaining power. Reference: CIPS Level 4, Market Power Analysis.