I haven't used them myself, but have read some good things about Tours By Locals, an outfit in the Seattle area who screens local guides in different areas. I believe they charge in US $, they charge you and then they pay the guide. We were looking into a trip in Morrocco, where the guide said he could take up to 10 people, but we booked something else instead.

Here's a list of their tours in Paris, which are all done by locals:
http://www.toursbylocals.com/TBL/Web...tfRseTHAsDT2E0

You may want to check tripadvisor.com for further info on Tours By Locals.