A checkbox when posting to denote that content was influenced by provision of gift/service. Then the platform (Instagram, for example) has a subtle but recognis

A checkbox when posting to denote that content was influenced by provision of gift/service. Then the platform (Instagram, for example) has a subtle but recognisable mark on that photo or caption. Threat of fines for non-compliance, but only really police the main users so they lead by example. Make it easier and less damaging to comply for the major users than to avoid it. Make it like the cachet associated with being "sponsored" in extreme sports so smalltime users aspire to follow suit.