How would you handle multiple 'On-Call' requests during the same time period?
Example: 3 clients want you to be on call 24 hours on the same day. For simplicity assume the rate is $10 and you don't mind being on call the requested day.
Would you charge all 3 a retainer of $240 = $720?
Would you agree to be on call with the first client and tell the others you can't do it because your on call for someone else?
One thing to worry about is if you agree to be on call with more than one client, 3 clients can call around the same time. How would you handle that or set expectations beforehand?