You can sign up for one of the multiple marketplaces for influencers and see all the metrics. I've seen simple things like number of followers, videos, views, comments, length of video, etc. The category their YouTube channel is in. Related stats on their other social media like Facebook and IG, etc.
The one I used, you put up an ad of your product, and influencers applied, so you could quickly vet them by easily going through the data in one place.
The one I used, you put up an ad of your product, and influencers applied, so you could quickly vet them by easily going through the data in one place.