They aren't reporting anything yet. What we hearing is just from news media who get their leaks/info from investors who get some form of IR reports/ presentation.

Both will do public reporting only when they IPO[4] and have regulatory requirement to do so every quarter. For private companies[1] reporting to investors there are no fixed rules really[3]

Even for public companies, there is fair amount of leeway on how GAAP[2]expects recognize revenue. The two ways you highlight is how you account for GMV- Gross Merchandise Value.

The operating margin becomes very less so multiples on absolute revenue gets impacted when you consider GMV as revenue.

For example if you consider GMV in revenue then AMZN only trades at ~3x ($2.25T/$~800B )to say MSFT($2.75T/$300B) and GOOG ($3.4T/$400B) who both trade at 9x their revenue.

While roughly similar in maturity, size, growth potential and even large overlap of directly competing businesses, there is huge (3x / 9x) difference because AMZN's number includes with GMV in retail that GOOG and MSFT do not have in same size in theirs.

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[1] There are still a lot of rules reporting to IRS and other government entities, but that information we (and news media) get is from investors not leaks from government reporting - which would be typically be private and illegal to disclose to public.

[2] And the Big 4 who sign off on the audit for companies prefer to account for it.

[3] As long as it is not explicit fraud or cooking the books, i.e. they are transparent about their methods.

[4] Strictly this would be covered in the prospectus(S-1) few weeks before going public and that is first real look we get into the details.