Google's Human Quality Evaluation:

The Google testers are paid $10 - $20 for each hour they filter the results of Google. Payment is done through Payroll. The international agents are instructed by the Human Quality Evaluation Team of Google. How does Google decide if a site is offensive or not?

Google's Human Quality Evaluation: How To Spot Offensive Sites & Google's Whitelist - Henk van Ess's Search Bistro