Purchase Price and Value - who to trust?

I want to seriously start doing some searching for properties, and have been told I need to really consider keeping the purchase price around 70% of the value. BUT - the question is this: who to trust? I'll start with my house for example:

the appraisal district website shows our house at nearly $119k. Zillow.com shows us at $138k. It is 4bdrm/2.5 bath, 2050 sq ft 2 story home built in 2004.

There are 3 houses in our area with comparable sizing and stats between 114-134k.

So the question is, who/what do I trust? There is like a 25k spread here, and I just don't know what to be looking at.