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
Whenever you are considering using a website as a source, it is very important that you review the contents in detail.
There are many other resources to evaluate web pages. One of the more interesting examples is CSU Chico's CRAAP Test.