Know that you are working with the best.
I use FreshBooks as my little accountant in the cloud. This means that every client big or small can pay directly through the invoice they receive. Once you receive that invoice you have the option to either pay using card or ACH secure bank transfer.
Some projects may require a signed contract before any design work is started. This covers both you and me!
Received an Invoice and not sure how to pay? here is a helpful article