You don't have to employ AI/human differentiation (e.g. captcha) if you statistically mine user actions. I think that's where resolution is more likely to come

You don't have to employ AI/human differentiation (e.g. captcha) if you statistically mine user actions. I think that's where resolution is more likely to come from. By definition, shill accounts have different patterns than normal user accounts. Step 1) Deal with new accounts (preferably in an anonymous way). Step 2) Mine the actions of older accounts to detect patterns that point back to shilling. Not insurmountable.