What got me was the ex customer was offended when I asked why employ those you clearly do not trust - since it was not a remove the temptation type of inquiry, but how to keep out those he already knew were not trustworthy. Had to be one of those "setup someone else to blame" situations.
I have no history of needing to work with untrustworthy employees to relate to, as the couple I had who were untrustworthy, were made ex employees at the moment trust was gone.
'Tis the life of providing support. One time, you are too "dry" for only answering exactly what is asked, in as short and direct manner as possible. The next, you are butting in when you read between the lines, and talk to the person as if they were standing next to you. Sucesfully reading/guessing/lucking into the intent of the other party is the money zone...
For Sailor. References are fairly worthless these days, as the former employer wants to cover themselves. Background checks are not fool proof, not even if just looking for the big issues. (Have experience with checking volunteers for a national org, and all they really do is allow the org to say they tried to find issues.) To me, the best is to start with a safe position and get to know the person before adding more responsibility. Yes, you do what you can to check, but you cannot reply on those checks, or always eliminate people because of one item in their past. In other words a reference background check is no better than buying a used car based solely on carfax, since both rely on the reporter to actually report, and when they do, to report correctly. You still have to test drive the car, and the employee.