The supplier selection decision:

a$.$ should be based on quantifiable factors such as price and delivery, and ignore social and political issues.

b$.$ can be seen as a decision making process undertaken in an environment of certainty.

c$.$ is based on a uniform set of weighted criteria that can be applied to every purchase.

d$.$ can be depicted by a decision tree identifying options, evaluation criteria, and probabilities of success and failure.

should always be preceded by a formal supplier evaluation and rating.