> Like if someone says we have this many users as a statement you have no idea what they are actually calculating

I think that's BS. User metrics are usually very explicitly defined (e.g. monthly or daily active users have always been clearly defined wherever I've worked, even if just for the sole reason that people collecting those numbers need to know what to count). User quality is definitely a gray area and estimating bot percentage has become increasingly difficult, but user metrics are not some ill-defined, fuzzy math notion.

Right I'm not saying that Zuck's staff doesn't know how to calculate MAU or ARR. I'm saying I'm not sure we can trust the 'median' (median on a scale of super-scrupulous to outright-dishonest) CEO is not counting things like inactive cohorts, newsletter subscribers, website hits when counting 'users'... or being very optimistic about whether a customer will renew when calculating 'recurring revenue'

I may be wrong! But I am definitely giving such claims the side-eye

Seems like your “increasingly difficult” part is kinda what they meant.

This is an area where deception is possible. For example, if the metric is background API calls, you can fake that too. What matters is how you define 'active users.' In fact, this is a common technique used in well known scam apps in Korea, often called 'vanity metrics.' Generating abusive users and background traffic that create no real business value, then packaging it as user growth. There are even people who specialize in this.

if someone says they have a billion users because they are connected to the doubleclick exchange... they aren't lying, they might be deceptive or simply foolish.

As part of due diligence, the buyer/investor should ask how these numbers are calculated and make their own judgement. Unfortunately I believe startups select for those who dance the border of deceptive and foolish.