Sure, but it's not about identifying whether an ad was paid for, it's about identifying ads. People are understandably not aware that most of what they see is an ad. Most product reviews are ads. Most "best X" articles are just ads. Most news articles about products are ads. Even on social media, a non-zero number of people's posts are just ads. Some of this is illegal, but even then the consequences are so low that we end up with articles like the above where Google pays next to nothing for the infraction.