In the context of ExtremeMarketing and ExtremeSales, the PurchasingAgent is someone who collects requirements from others and acts as an agent to buy what's needed from suppliers.
PurchasingAgents are most valuable when they are dealing with large numbers of competing suppliers offering what are essentially commodities.
There can be a bewildering number of variables in such purchasing processes and good agents can save people a lot of time, frustration, and money.

Where the acquisition of software is treated like a commodity, a PurchasingAgent is supposed to get terms and conditions that meet the commodity expectations of the enterprise at as low a price as possible.
If you are marketing to PurchasingAgents, differentiation is generally a difficult topic.
MarketingMessages are treated by PurchasingAgents as largely empty noise.
They will, however, respond to in-depth discussions of real UserStory materials because good a PurchasingAgent purchases what their user needs.

ExtremeMarketing to a PurchasingAgent means NoMarketing.
It means providing simple, clear descriptions of the product, complete information about pricing, support, and upgrades, and a quality list of references.
That is ExtremeMarketing to this community.
Done well, they'll help you with the DecisionMakers, users, and TechnologyExecutives.
It is as important to the PurchasingAgent to buy your product and satisfy their user (client) as it is for you to sell them the product.
As agents, they need a lot of help brokering the deal.

 -- MartyHeyman