In 2015 as a whole, Google earned $74.5 billion in revenue with $23.4 billion of operating income (profit before interest and taxes).
The search engine part of Google's business 'crowdsources' free labour in various ways including:
To date, Google is not very good at detecting all the sites which have paid and sponsored backlinks (this is against their guidelines).
Google encourages the Search Engine Optimisation community to report them here:
This may be considered part of the day-to-day work of a SEO consultant working in a Google-dominated market. For example I have detected & reported well over 100 of one my client's competitors for selling or buying paid links. Reporting does not often appear to have any noticeable effects based on over 4 years experience!
Google encourages the Search Engine Optimisation / PPC community to report them here: https://support.google.com/adwords/contact/thirdparty_complaint
I have seen ads phising for Google Account details bidding on the name of Google Keyword Planner tool!!!???
Google encourages the online community to report violations of their Map guidelines here: https://support.google.com/maps/answer/3094088.
Google encourages the community if they find a review that they think violates Google review policies, (https://support.google.com/plus/answer/2622994) to use the “Flag as inappropriate” link next to a review. https://support.google.com/business/answer/4596773?hl=en.
This again may be considered part of the day-to-day activities of a SEO consultant doing client competitor analyses working in a Google dominated market .
In the final analysis, the Google Web & Map Spam / Adwords policy contravention / Paid Link reporting tools above are fundamentally just free labour for Google from people who don't work for them (like SEOs and the online community!), like the link disavowal tool for sites affected by the Google update known as Penguin - a tool that enables webmasters to disavow (i.e. ask Google to ignore) links to their sites. This effectively creates via Penguin a list / feedback loop of low quality sites & links for Google to check their Penguin and Panda algorithm updates against!
Also there's https://topcontributor.withgoogle.com, https://www.google.com/local/guides/ & the largely unknown army of volunteers called Mappers (proposing and approving edits to Google Maps, with assistance from Google)...
There's even a Google app called Crowdsource asking users to perform tasks to improve the quality of services like Google Maps, translation, image transcription etc. The app, unsurprisingly, doesn’t offer rewards of any kind! Say no more!
They should compensate this work! Gis a job!