Are you paying your agent for travel services on account or by means of a charge card? With all agents increasingly obliged to manage (and reduce) their cost of sale there is a tangible cost in extending a credit facility to the client. This will have to be factored in to the agents costs.
The use of a card system (Air Plus, American Express, Diners Club etc) offers a series of benefits including extended credit which obviously represents a saving. However, in addition to that Millennium Corporate Travel can usually acknowledge a reduction of costs for those clients who pay by card.