There are an estimated 25 million safe deposit boxes in America, and they operate in a legal gray zone within the highly regulated banking industry. There are no federal laws governing the boxes; no rules require banks to compensate customers if their property is stolen or destroyed.

Every year, a few hundred customers report to the authorities that valuable items — art, memorabilia, diamonds, jewelry, rare coins, stacks of cash — have disappeared from their safe deposit boxes.

But even when a bank is clearly at fault, customers rarely recover more than a small fraction of what they’ve lost — if they recover anything at all. The combination of lax regulations and customers not paying attention to the fine print of their box-leasing agreements allows many banks to deflect responsibility when valuables are damaged or go missing.

“The big banks fight tooth and nail, and prolong and delay — whatever it takes to wear people down,” said David P. McGuinn, the founder of Safe Deposit Specialists, an industry consulting firm. “The larger the claim, the more likely they are to battle it for years.”