The answer is simple, allow some level of user feedback from proven real users (for example, only people with gmail accounts that are over 5 years old and who use them at least 3 times per week to eliminate fakers—-but keep this a secret) and apply it mildly as a ranking signal.
As long as it doesn’t become the only factor in ranking, you still retain strong incentives to do all the old SEO stuff, yet with a layer of human sanity on top.