This is basically banking on someone else’s hardwork. The gardening company he gave an example does the hardwork of creating original content and reposters simply grab content of “independent” profiles and share it in their feed. Pulling in what little followers they have aswell because then that person will be like, “OMG I got featured, see guyss.”

If only these featured people knew that someone is making money off their work, paying them in “exposure” I wonder how many will explicitly give permission to repost.

About your original copyright question, it simply comes to down to getting explicit permission.

Instagram says, if you get written permission from a creator to repost their content, then you can do so.

Tagging doesn’t count as permission.