Limiting your search to specific domains (.edu or .gov) can remove some of the less reputable websites from your Google searches.
.com - commercial or business
.edu - educational institution
.org - organization (often non-profit)
.gov - government organization
When you are considering using a website as a source, it is very important that you review the contents in detail. An easy way to make a determination is to use Jim Kapoun's Five Criteria for Evaluating Web Pages:
There are many other resources to evaluate web pages. One of the more interesting examples is CSU Chico's CRAAP Test.