External users are not part of it. It's a "curated" model. IMDb clearly stakes their reputation on accuracy and comprehensive coverage. IMDb's TOS ensures that you relinquish all copyright claims and grant them an exclusive license to your content. IMDb won't cite their sources nor attribute contributors. They own and control everything on the site. Their rates for abuse and misinformation are unpublished. IMDb is an opaque, black box.
Wikipedia has a similar model for protecting articles known as "Pending Changes". Anyone can submit an edit to the article, but the revisions and new data is held back from the "front page" publication until approved by someone with the proper user rights. Almost anyone in good standing can obtain those rights, and it's 100% transparent. Every edit is reviewable by anyone with Internet access, every edit is attributed and licensed under CC-BY-SA. The servers, editors, and bots track and tag vandalism and other forms of abuse with public records. Verifiability is mandatory.