Marketing expert Rosalie Hamilton has this to say on expert witness retainers:
You should NOT empty your waiting room, re-arrange appointments, etc., to schedule deposition or courtroom time UNTIL you receive a check for the full, estimated time. Then, if they postpone or cancel, you can refund money on a sliding scale (see Fee Schedule and related info in The Expert Witnessing Marketing Book) based on how easy/difficult it is and based on the date of postponement/cancellation, how easy is it is for you to restore your local work schedule.
I hear this over and over, and experts should not experience loss of income due to dates being moved by the courts and the attorneys.
For more, see expertcommunications.com.