In evaluating the authenticity of an influencer’s audience, there are several reputable tools and platforms available. These include:

1. Followerwonk: This tool provides detailed analytics on Twitter followers, including their locations, the times they’re most active, and their most-used words. This can be incredibly useful for analyzing audience authenticity.

2. HypeAuditor: HypeAuditor offers a comprehensive report on an influencer’s audience, engagement, and content. It’s particularly known for its detailed audience quality analytics, which can help detect whether an influencer’s followers are genuine.

3. SocialBlade: SocialBlade is useful for getting a big-picture view of an influencer’s growth trends, engagement rates, and audience demographics. Irregular growth patterns could suggest inauthentic follower acquisition tactics.

4. Flinque: Flinque offers a robust Influencer Audience Authentification feature that audits the influencer’s followers, scrutinizing their engagement rates, quality, and bot-like activities. It also offers a larger suite of influencer marketing tools, making it a comprehensive solution for brands.

Choosing the right platform really depends on a brand or agency’s specific needs, budgets, and objectives. For detailed and reliable audience analysis, platforms like Flinque and HypeAuditor could be particularly useful. Meanwhile, Followerwonk and SocialBlade provide efficient insights specifically on Twitter and YouTube accounts respectively.

Several factors factor into assessing the authenticity of an influencer’s audience. These include but aren’t limited to follower engagement rates, growth patterns, locations, and follower-to-following ratios. Please remember, these tools provide helpful information, but human discernment is also essential. Happy influencer hunting!