You can pay with cash, eInterac (preferred for clients in Canada), cheque, or Paypal/credit card.
Small projects are paid in advance. For bigger projects, I send an invoice for the first half and payment of that first half is considered as the “go ahead.” Once I finish the document and send it back, the second half of the payment is due. For long-term projects, it is possible to arrange for payment in instalments.
On-going clients are issued an invoice at the end of the month for the work done that month.