I just got a tentative job offer to be a federal correctional officer (BOP), what do they check for?

They will know more about you than you know about yourself.

In general if they have not changed thier policy, they will physcially send agents out to talk to every neigbor you lived next to in the last 10 years. They will go in person and check with every job you held for 10 years.

They may go and talk to your college and/or high school teachers.

They will look at your credit report for the past 10 years, your diving record, and your criminal record ( assuming you do't have one.

You will have to take a complete physcial exam.

After you get the job you will normally do a week or two at the federal prison before you go to GLYNCO GA for some weeks of wonderful training.

It will have some wonderful memories.

Just about everything.
ME!!
everything...be wary of a hair test, goes back the longest. Consent to substance abuse testing usually is present on the application, so any acceptance to the offer would trigger this consent.
Just about everything going way back to when you became an adult
Just about everything. If they are like the California DOC, they only go back 7 years unless you have been convinced of a felony (which would preclude you for service).

Be honest ALWAYS. No one is perfect. Even devote Christians have a few fu**ups on their records.
they check everything