I'm currently only accepting payment via PayPal or Venmo for both commissioned work as well as print purchases. Shipping will be additional based on where it's going and will be calculated at the time of contacting me and knowing where it's being shipped. For commissioned pieces I ask for half of the cost up front to start the project. I will send you updates as the drawing progresses with a final photo of the finished piece. At that time I will ask for the remaining balance to be paid including shipping. I will then pack it up and send to the specified address. That's it. Easy peasy.
For print purchases I ask full price be paid up front, as I use a 3rd party to print and ultimately get invoiced for the prints.