Reliable and accurate database

[Peter Kim]

I'm sure one day I'll look at this post and laugh at my ignorance, but as of now I need your guy's help. 

The only source of "accurate" information on real estate properties I've used is Zillow. I've seen too many properties that are under priced for the location and once I speak with the owner directly, the monthly mortgage is a few hundred dollars higher etc, etc. 

What are the most reliable and accurate mass databases for on sale properties?

Thank you everyone!