Track the individual cars sold by Carvana on a daily basis. Backtesting the results show that you can get within 99.9% of the company's reported sales figures.
Apple Store Rating Dataset
Thinknum’s Apple Store Ratings dataset provides insight into mobile app ratings that are available in Apple’s App Store. The metrics in this dataset include rating, rating count, app version, as well as the app’s price. These metrics can be used as a proxy for download count as well as, tracking the quality of an app over time.