"On the Internet, nobody knows you're a dog." - Peter Steiner
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. 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 easily accessible through the Web. One of the more interesting examples is CSU Chico's CRAAP Test.
When searching Google, you can click on the Settings link in the lower right corn to access the "Advanced Search" limit your search results to educational or government sites under site or domain.
Try these Google Advanced Search Tips and Tricks