Speakers are people, too, and there are often scheduling difficulties or personal issues that prevent a speaker from accepting your invitation. These are factors that are beyond your control.
This can be especially frustrating, but it is important not to dwell on the rejection. While you may have been dreaming about featuring this speaker, there are indeed other people that can make your event shine. Here is a list of things you can do to handle these situations:
Step 1: Thank them sincerely
Be understanding and thank them for considering this opportunity. If this is a high-value speaker, you might also want to consider them for future events as well.
Step 2: Ask for clarification
Kindly ask the speaker what exactly caused them to turn your event down. Once you know the reason for their decision, see if there's anything you can change to make it more convenient for them. This information may help you when you are inviting future speakers.
Step 3: Ask for a recommendation
Well-connected professionals usually have a network of people that can be a good match for your event. If it feels appropriate, you could also ask them if they could recommend other speakers for your event.