A simple scenario:
The DM wishes to break a cleric's concentration on their bless spell, and a foe uses suggestion to tell the cleric to cast silence on an enemy spellcaster. The rationale is that this would prevent enemy AoE spells from affecting frontliners.
The PC rejects this, saying "No, my PC thinks that's unreasonable and continues to concentrate on bless instead."
In such a case, who gets the say whether the suggestion is or is not reasonable? Or should it be determined by a Persuasion roll? How can the DM give a fair ruling that doesn't take away the player's agency, but at the same time does not allow the player to freely deny the effects of suggestion?
The rationale is assumed to be "50-50".
This question is different from this suggested duplicate, as this is specifically asking for guidance on how to give a fair ruling that the suggestion will fail/succeed when the spell is cast on a PC, which may result in agency being taken away from the player.