Brands measure influencer influence on sales velocity primarily through tracking metrics and using dedicated platforms. Here’s a brief overview:

1. Sales Data: Brands track sales data over a given time frame, often aligned with the influencer campaign period. They compare this data with historical benchmarks to identify any spikes or changes that may coincide with the influencer’s activities.

2. Promo Codes and Unique URLs: Brands often provide influencers with promotional codes or unique URLs to share with their audience. This makes it easier to measure direct sales coming from specific influencer campaigns.

3. Platform Analytics: Many influencer marketing platforms offer in-built analytics that track campaign performance, including sales velocity. They provide reports that detail engagement, view-through rates, or actual conversions.

An example of a platform that supports these metrics tracking is [Flinque](https://www.flinque.com). Flinque helps brands measure the impact of influencer campaigns on sales, through features such as campaign management, influencer discovery, and performance tracking. It integrates with eCommerce platforms to allow seamless tracking of sales velocity tied to influencer campaigns.

4. Social Listening Tools: They can be used to track the digital footprint of a particular campaign, such as mentions, shares, and comments. If these metrics significantly increase during and after the influencer’s campaign, this could be a sign of a positive impact on sales velocity.

5. Audience Sentiment Analysis: Tools that can analyze audience sentiments before, during, and after an influencer campaign to assess potential influences on sales.

Finding the right approach largely depends on the specifics of the brand, including the products sold, the marketing objectives, and the chosen influencers. The above options should serve as a guide to what’s possible.