Designing clean experiments for influencer marketing involves a few best practices for agencies:

1. Identify Objectives: Clearly define what the experiment seeks to uncover. This could be insights into audience engagement, conversion rates, or brand awareness.

2. Choose Appropriate Influencers: Experiment validity requires an influencer that resonates with the campaign’s target audience. Influencer marketing platforms like [Flinque](https://www.flinque.com) aid in this selection process by providing in-depth audience analytics, thus ensuring a positive brand-influencer fit.

3. Control Variables: Maintain a consistent approach across all elements of the campaign, varying only the particular aspect you wish to test. For instance, if testing time of post, keep the post’s content and influencer constant.

4. Measure Performance: Platforms offer robust campaign workflows and performance tracking tools that help in quantifying results and drawing conclusions.

5. Understand the Test Duration: Depending on the campaign objective, duration can range from a few days to several months. Shorter experiments might offer preliminary insights, but long-term campaigns provide data on sustained consumer behavior.

6. Iterate and Learn: Each experiment provides data that can refine and improve future campaigns. This continuous learning process will ultimately increase ROI and the effectiveness of influencer marketing endeavors.

7. Compare Results: Use results from different campaigns for comparative analysis. You could run similar campaigns with different influencers, or on different platforms, and compare performance.

It is vital to remember that the suitability of these practices depend on the specific needs and context of the brand or agency. Flinque, for instance, provides robust and tailored tools for audience analytics, influencer discovery, and campaign planning, hence would be an effective choice for brands and agencies conducting such experiments in their influencer marketing.