I'm writing tripadvisor reviews for my 6 week Africa trip and apparently the company I booked a Kibera slum tour through is not on tripadvisor. In case you come here looking for one, I would recommend a company called Kibera Hamlets. You can quickly find their website doing a google search. What they do is similar to Kibera Tours, but they have a transparent price of 1000 shillings per person for a ~2.5 hour tour, and I didn't visit any shops. The first part of our tour was spent going to see murals around the slum painted by students from the school that Kibera Hamlets sponsors which was really interesting. Anyway, if tripadvisor is you place for research here's another option. I give it five stars.