Want a graphic illustration of how banks can manipulate their books to multiply their profits from your mistakes? The Pew Health Group, which has been pushing for more transparency and better consumer protections on checking-account fees, designed this interactive chart (below) to show how a bank can re-order your transactions to maximize overdraft fees.
You can click to see how that happened on a single day to one account-holder at Wells Fargo, Veronica Gutierrez, whose case prompted a federal judge to order the return of $200 million to customers and accuse the bank of "gouging and profiteering." (I wrote about the case here.) She made a single purchase that she had insufficient funds to cover, and the bank turned it into four overdraft fees, quadrupling its return from $22 to $88.
The problem's impact has been lessened somewhat now that banks have to get customers' permission to allow debit-card overdrafts at all. If you decline the option - a sensible choice, because otherwise you're turning a debit card into a credit card - your transaction will simply be refused.
But most banks are still urging customers to sign up for the supposed "protection" this provides. Pew's graphic is a good illustration of why it's such a bad idea - especially if banks continue to be able to engineer their bookkeeping to maximize the costs of your errors.