Respond to everything human, fast. DMs especially: a message about your service is a LEAD, and social inboxes are where slow response quietly kills demand you paid to create. Bots and spam earn deletion, not dialogue.
Negative comments split into two species: legitimate gripes get the review-response treatment in public (professional, specific, move it offline: 'call us and we'll make it right'). The audience is every future customer watching how you handle heat. Trolls get one calm factual reply maximum, then hide/restrict; feeding them is content for their account, not yours.
Never delete honest criticism (screenshots make deletion the story). But do delete abuse, slurs, and spam without guilt. Your page, your shop floor.