By ease of use, how long users stay in website and come back to click other link, people sentiment on internet about website (this is not a 100% solution, as we have already seen with counterfeit product ratings in Amazon), but excessive backlinks post 2010 era should signal that something is not going well here.

I know some agencies reached us to help with SEO and they were proud to show us that they ranked 1st in some keywords and submitted their reports how they achieved, you would be surprised, they literally created 100s of single page websites/presentations in wix, weebly, canva and many other websites to create single backlink, now google thinks they should be ranked 1st. A lot of SEO people seems doing this, and only excuse is, others are doing that as well.

Human content curation/ranking?

I have no much hope for algos, nor for AI. People will find ways to hack and fool them forever.