It is completely up to you, and the decision is on an account by account basis. You can setup your client accounts (uniquely) with either your credit card (and your info in the client profile) or their credit card (and their info in the client profile). This will determine which bills get charge to whom and who receives the email/PDF invoices for campaigns. If you’re client receives the bills through Postalytics, the emails and PDFs will use the branding you setup in the Agency Account, rather than Postalytics branding.