Comment by fumar

Facebook is the least transparent ecosystem. As a marketer, I find it hard to invest dollars without being able to see or understand what percent of custom audiences are exposed to ads. For example, one can upload a file (list of emails) to a custom audience, lets say 1 M big, for FB to ingest. Voila your audience is active for targeting, but how many of those emails (users) will be targeted, who knows. FB's inventory is overpriced and untraceable.