I do this once or twice a month through SF City Guides, a volunteer program of the SF Public Library. Annie and I took a dozen of their tours before signing up for the training last year. They have high standards for the content of the tours and for effective communication from the guides. Many of our walkers say that's what keeps them coming back.
We offer more than 60 tours of different parts of San Francisco, and they are free of charge, though donations are accepted to keep the website up and running and pay our two employees. We guides take no pay and accept no tips. I don't know why we would when we're having so much fun and meeting such interesting people.