A bank I was with years ago was caught being a major douche. Evidence and testimony by employees verified what everyone thought and they were eventually sued for:
They purposefully held deposits on accounts that are always low. They would accumulate the day's checks for the account, and work out what order of cashing them produced the highest number of bounced checks for the account. They would then process it that way, assess the fees and penalties, THEN let the deposit go into the severely negative account.
People getting paid expecting a $300 deposit found themselves at -$300 and wondering what the hell happened.
Many people living paycheck to paycheck found themselves unable to eat, pay rent, or worse all the time.