A look-the-other-way attitude at some U.S. hospitals may be fostering a black-market trade in kidneys, transplant experts say.

Some hospitals do not inquire very deeply into the source of the organs they transplant because such operations can be highly lucrative, according to some insiders. A single operation can bring in tens of thousands of dollars for a hospital and its doctors.

Despite guidelines from various groups and Medicare, U.S. transplant centers are mostly free to write their own rules for screening donors to make sure they are not selling their organs. The questions they ask vary widely. Some hospitals require long waiting periods to weed out shady donors; others don’t.

“Some have a pretty cursory examination, like, ‘Are you sure you want to do this?'” said Art Caplan, a University of Pennsylvania medical ethicist involved in a U.N. task force on international organ trafficking. “Some don’t look very hard.”

The possibility that organ trafficking is going on in the U.S. — and that the surgery took place at hospitals in this country — was raised last week with the arrest of Levy Izhak Rosenbaum in an FBI sting.

The New York man was charged with plotting to buy a kidney from an Israeli and sell it to an American patient for $160,000. Prosecutors said Rosenbaum was secretly recorded boasting that he had brokered “quite a lot” of transplants over 10 years.

If the allegations are true, it would be the first documented case of organ trafficking in the U.S. and would confirm something many medical insiders long suspected was going on, transplant experts said.

Buying or selling organs is illegal in the U.S. and nearly everywhere else in the world. But there is a thriving international black market because demand far outstrips supply. In the United States alone last year, 4,540 people died awaiting kidneys.

In the sting, an undercover federal agent posed as a secretary seeking a kidney for a fictitious uncle. No surgery took place.

Mark McCarren, a New Jersey federal prosecutor involved in the case, said Rosenbaum indicated that the transplants he brokered took place at more than one U.S. hospital and that the hospitals were duped and were not in on the scheme.

According to prosecutors, Rosenbaum was shockingly familiar with the U.S. system and how to beat it. Sellers and recipients would concoct stories about being relatives or friends to fool hospitals into thinking no money was changing hands, McCarren said.

Medicare, which pays for some organ transplants, requires hospitals to have someone evaluate living donors to make sure they understand the process and aren’t being coerced or paid. Violators risk losing Medicare dollars.

On average, a kidney transplant in the U.S. resulted in $259,000 in medical bills last year, according to the Milliman consulting firm. Hospitals and doctors are reimbursed an average of $80,000 to $100,000 by private insurers, said transplant specialist Dr. Thomas Diflo of New York University.