There are any number of factors that can be included in a Vendor Classification System, depending on the nature of your business and what you consider important about relationships with vendors.
Some vendors are more important than others.
Now, just about anything that is said here about the relative importance of one type of vendor over another is likely to be offensive to someone. Consider, for instance, the situation of a small manufacturing company known to your author here in central Nebraska. The company, PMZ, Inc., produces a short line of 14 consumer products that are assembled on piece rate and sold to women's fashion wholesalers and mass market retailers throughout North America. The products manufactured are themselves assembled from components made by other manufacturers throughout the United States. In fact, in order to produce the 14 products and two display groupings offered by the company, materials and components must be ordered from over 45 separate suppliers throughout the nation.