For npm, trust isn't really a concept. The repository is just a channel used to publish packages, they don't accept any responsibility for anything published, which is fair considering they allow anyone to publish for free. There are no mechanisms in npm that can help you verify the origin of a package and point to a publicly available source code repository or that ensures that the account owner was actually the person who published the package.
Security and trust is very hard, but my point here is that npm does nothing to facilitate either, making it very difficult for the average developer to be aware of any issues. The one tool you get with npm is...not really working the way it was supposed to.[2]
1 - https://reproducible-builds.org/ 2 - https://news.ycombinator.com/item?id=27761334