That's why Bloomberg discloses the sponsored posts on Instagram as: (yes this was really sponsored by @mikebloomberg) in the description.
The entire message is often ironic, so other nonsponsored people are also using (yes this was really sponsored by @mikebloomberg) in their posts to make fun of Bloomberg, so although everyone is disclosing they're being paid, you don't actually know if someone is being paid or not.