It's very driver dependent. Sometimes I'll get the super professional, uniformed delivery driver driving a marked van who seems to actually care about doing a good job at his job. Other times it'll be the guy in jeans and a t-shirt who throws the package on to the porch from 8 feet away before going back to their nearly broken down white rental van. Both get the picture before leaving though.

My guess is one of two things, either Amazon contracts out overflow work, or some of the contracting companies have high employment standards and some don't.