$75,000 to love a brand on Instagram — is it an ad?

The millions of people who follow Kim Kardashian West and her sisters on social media have become accustomed to seeing them praise everything from fatburning tea to gummy vitamins for healthier hair.

“Ever since I started taking two sugarbearhair a day, my hair has been fuller and stronger than ever!! Even with all the heat and bleaching I do to it!” Khloé Kardashian posted on Instagram this month.

But in the last week, close watchers of the sisters’ accounts may have noticed a small addition to those laudatory messages about the latest miracle product: “.ad.”

For marketers contending with consumers who use ad blockers online and have cut the cord to their TVs in favor of streaming services, social media has become a way to reach an elusive audience. Brands such as Jack in the Box and Red Bull have proved willing to pay thousands of dollars per social media mention to people like the Kardashians and other so-called influencers who command big, loyal followings on services like Instagram, Snapchat and YouTube.

These mentions, however, are often presented as testimonials rather than advertisements, a practice that at least one consumer advocacy group has claimed is deceptive. And the Federal Trade Commission has found itself struggling to articulate exactly how these sorts of paid brand endorsements should be handled to ensure that they are identified as ads.

In the case of West and her sisters, Khloé and Kourtney Kardashian and Kylie and Kendall Jenner, TruthinAdvertising.org, a nonprofit that fights deceptive advertising, asserted that dozens of Instagram posts from the sisters violated guidelines from the FTC that say it should be “clear and conspicuous” to consumers if a person endorsing a product “has been paid or given something of value.” However, while the agency suggests putting “.ad” or “.sponsored” at the start of those kinds of social media posts, or providing verbal disclosures in videos, there are no hard and fast rules.

“We’re not prescriptive about that,” said Mary K. Engle, the FTC’s associate director for advertising practices. “But it has to be unambiguous.”

For example, simply saying “thank you” to a brand or adding “.sp” or “.spon” probably isn’t clear enough, while saying a brand is a “partner” probably is, she said.

Disclosure, which the FTC has been wrestling with for years, has become more important as the money offered to influencers has jumped and the number of sponsored posts on services like Instagram and YouTube has surged.

Captiv8, a company that connects brands to influencers, says someone with 3 million to 7 million followers can charge, on average, $187,500 for a post on YouTube, $75,000 for a post on Instagram or Snapchat and $30,000 for a post on Twitter. For influencers with 50,000 to 500,000 followers, the average is $2,500 for YouTube, $1,000 for Instagram or Snapchat and $400 for Twitter.