This is a question we deal with daily. We operate a very simple system based on a fee for service. There are no commissions or hidden costs involved. An estimate of the total job is quoted to you by phone or email. Download a copy of our rates here. On completion of the work, an invoice is sent to you for payment by cash, bank transfer, cheque, money order, PayPal or credit card.
For ongoing secretarial/virtual assistant support, whether it is for 10 hrs a week, etc., a retainer agreement can be arranged.
Contact me at firstname.lastname@example.org to discuss further.