A while ago I bought a shoutout through @velvetcoke on insta. My client at the time was a musician looking to increase his online presence and up their spotify plays. One shoutout led to 2,000 plays on spotify. The ad was simply a reshare of his Spotify page with the link attached.
I knew to choose their account for a shoutout because of their reach and content. Also, the target audience overlapped with mine.
ADVICE
Remember, you can always ask for metrics. I've interacted with accounts who don't provide metrics. I don't prefer them because sure they may have 20k+ followers, but the likes on their posts are usually 30 max. This is a sign they most likely bought followers since not many are interacting with the posts.
Accounts like the one mentioned above has over 60k likes on posts, showing me people actually interact with the page.