It may seem logical that purchasing carpet by itself, as opposed to through a qualified flooring professional, would result in a lower cost. However, carpet is not a stand-alone product. There are many additional services and expenses required to complete an installation project properly. A lower price does not necessarily mean a lower cost.
A recent national survey confirmed the increased expense of carpet as an exclusive purchase and explored the origins of these costs. The survey examined several components of carpet installation ranging from material price to management time to simple cost per square yard. The following table details these elements based on an average installation of 1,000 square yards. The resulting cost increase was between $3.55 and $7.21 per square yard.
http://www.starnetflooring.com/wp-content/uploads/2010/03/vol7_1.pdf
Link to Starnet Starlog Volume VII issue 1 below.