Can the other person decline to be a Collaborator?

The short answer is no. You can not decline to be added as a collaborator, however, once added, you can then go into the task and remove yourself from being a collaborator. Just make sure this is what you want to do because you can not reverse this action. The Assignor added you for a reason. You might want to check with that person to see why they added you if you don't think you are relevant to the task.

To remove yourself or someone else from being a collaborator:

1. Locate and open up the task that you are a Collaborator on.
2. Click the Collaborators tab in the Task detail screen.
3. A list of collaborators will open up.
4. Click on the trash can to the right end of the name you wish to remove.
5. Click the red Yes, Delete button.
6. Click Close.