Ask the best people you’ve ever worked with who the best people they’ve worked with are. Recurse. When names start repeating through different graph paths, make those people an offer they can’t refuse. Once they join, ask them to do the same, and give them the budget and role to make it happen.

Unless you're hiring for rare roles that require niche skills, it's unlikely that you'll get people that are in overlapping networks. If you do, you might be encountering the problem where Company A has a bunch of people that used to work at Company B. Now Company A is just an "old boys club" from Company B and is biased towards their old colleagues.

If you ask for single referrals, how do you combat the problem of people just recommended people based on friendships and not actually work quality?

The best people I've ever worked with and the best people they've worked with all have good jobs at all times. You have to have a mechanism for matching with people who are actually interested in a new job.

Is this really battle-tested, as in: did you see this work in practice or do you have a reliable source?

Or is this something you came up with?