But that assumption is usually wrong. In reality, the purchasing manager will be more of an obstacle than a help . . . provided that is, that you are selling anything other than commodities.
More often than not, that department will have clear authority only to say No — at least with respect to a new product, service, or idea.
In most organizations, purchasing's actual role is to coordinate buying of known commodities. If you're selling copy paper, or paint, or any other kind of standard item, then the purchasing manager, or someone in the purchasing office probably is the place to begin.
But if you're selling something innovative (either because it's a new idea or new product, or because it accomplishes the job in a new way), then you'll be best to find your way to the actual potential user and create the sense of need at that level.
Unconvinced? Project yourself back a couple of decades, and imagine that you were selling one of the first personal computers. If you had started with the purchasing, the people there might have said, "Well, we do have a mandate to buy a dozen Selectric typewriters, and a dozen adding machines. But this strange-looking box you're offering clearly isn't a Selectric, and it doesn't fit the specifications we've set up for the adding machine, so we're not interested. Sorry."
But suppose, instead, you had found your way to the head of the engineering department, or to someone in the legal department who had endless versions of the same form to grind out, and had shown just what your little computer could do, then they probably would have found a way to open the necessary doors for you.
That's why I suggest you use the Purchasing Manager and Purchasing Department only as a last resort.
The same goes for the Personnel Department, if you're marketing your services. Instead, find your way to the person or department with the actual need.
For anything innovative or novel, Purchasing and Personnel Managers probably lack Authority to buy. Purchasing certainly lacks Need, unless your product happens to be relevant to the Purchasing area. And that department has Dollars only within prescribed limits.