Two offers with different prices may have a different convenience than the one suggested by the price list. Minimum order, frequency of deliveries, defects and management of emergencies affect the overall cost incurred by the company.
A hypothetical example is an economic supplier that requires large quantities. Unit savings can be accompanied by more immobilized money and hard-to-sell stocks. A more expensive but flexible supply might be preferable for an uncertain demand; the comparison depends on the actual conditions.
I propose to record delays, missing quantities and quality problems over a consistent period. A difficult delivery is not enough to describe a relationship, but a series of anomalies deserve a deepening. It is useful to distinguish supplier problems from errors in the prediction or internal order.
The choice should also consider how easily the supply can be replaced. For critical products, the presence of a viable alternative can have organizational value. The business relationship improves when expectations and information are clear: times communicated, reporting modalities and responsibilities in the correction. The price remains important, along with the ability of the supply to support the service promised to the customer.