How do sponsors measure and value social media posts?

Sponsors use a cost per engagement model based on what brands and agencies actually spend on advertising campaigns (not just platform rate cards). They look at followers, engagement (comments, shares, retweets), video views, and engagement rate. Most importantly, they score promotion quality on a 0-100% scale - examining whether other brands were promoted alongside theirs, how the brand was represented, and whether it seemed authentic. Posts with multiple brands get their promotion quality 'hammered' and each brand receives less value.