Bank tellers are constantly surveilled by cameras, security guards, and several-times-daily cash counting, and it's still easy to find accounts of them having stolen significant amounts of money before getting caught. These are all from within the last year:

Vannia Chatt: https://6abc.com/post/former-citizens-bank-teller-accused-st...

Karen Farrell Tigler: https://www.irs.gov/compliance/criminal-investigation/former...

Stephanie Rose Kilbert: https://people.com/bank-teller-stole-money-while-pretending-...

Derek Aut: https://www.justice.gov/usao-ma/pr/former-bank-teller-arrest... https://www.usatoday.com/story/news/nation/2025/03/28/boston...

Mountee Brown: https://www.justice.gov/usao-md/pr/maryland-bank-teller-plea...

Being US citizens doesn't make people incorruptible. In fact, many other countries are less corrupt than the US. Someone in this very thread reports having witnessed bank tellers getting bribed in one of those countries: https://news.ycombinator.com/item?id=43996765

I've been through a background check designed to screen out people who were vulnerable to bribery. They interviewed my friends and family from the previous several years to find out if I was secretly gay, cheated on my wife, gambled, drank too much, used illegal drugs, or had money problems for some other reason. It took about a year. I think it would be hard for a financial institution to be economically competitive doing that kind of thing with their call-center workers, because their customers can't tell if they're secure or not, just how much their services cost.