Pre-Employment Background checks

I'm thinking of branching out and using my security training to get my feet wet and offering Pre-Employment background checks and skip tracing as a service.

I've spoken to a few friends and associates who work in human resources working for small and large companies and they all outsource this to an outside company.

Just wondering how many of you do background checks of your hires, and if so how detailed are you in what you are looking for?
Do you also do drug screening as part of the process?

Interested in hearing how others handle this and if you use outside services.
Thanks