This is a really interesting question.
I would definately say that a background check gets done with employees.
With agents, I had not really thought that much about it to be honest. I think I was less concerned in that area since they are not an employee and I can part with them whenever I feel it is appropriate.
However, to get more to the point of your question, there are a number of online services that will do background checks for you. These seem to range from $50 to several hundred.
In the past when I have done background investigations on individuals, I paid a local private investigator to do the work. I paid him $125 per check.
His work was always very good so I considered it money well spent.
I would imagine you could do the same yourself with any local investigator. Let me suggest you shop around. I already had a pre-existing relationship with this investigator so I knew how he worked, but there are lots of Private Investigators who sadly are not as competent.
Here are a few online resources:
http://www.people-search.com/BackgroundCheck.htm http://safespy.net/backgroundchecks_more.htm http://www.searchrecords.org R