One caution, because I overcorrected. A flat no with no reason and no alternative, delivered upward to someone who does not know you well, reads as disengagement rather than as a boundary.
What fixed it was the trade version in the post. Same refusal, but it shows you are still holding the priorities, and it reads as competence rather than as refusal.
Downward and sideways, plain no is fine. Upward, hand back the choice.