Trulia's business model from the start was to aggregate listings from Brokerages and agents websites. They've added tax records to the mix but still do not get data from the multiple listing services.
If you really want to know what is for sale in an area hook upp with a professional in the area. Not only do we have access to the MLS, which carries the largest bulk of available properties but some of us know of FSBO properties and properties that are coming on the market.
The public has the ability to access the SF MLS. The only confusing part is the district subdistrict codes needed but there is a map on line that will give you that info also. (below) It is interactive so click on the area of the City then zero in on the sub-district.
If you need help contact me through my profile.