THE statue, Apollo the Lizard Slayer, was stunning. The five-foot-tall bronze, created by the Greek artist Praxiteles as many as 2,350 years ago, depicts the nude god poised to ambush a lizard.

Ali Aboutaam, above, and his brother, Hicham, bottom, are prominent antiquities dealers who say they are being more rigorous in tracing the history of the pieces that they sell from their high-end galleries in Manhattan and Geneva.

And the Cleveland Museum of Art wanted it. During a visit to Geneva in 2003, Michael Bennett, the museum’s curator of Greek and Roman art, noticed a statue beneath a black cloth while browsing at Phoenix Ancient Art, an exclusive antiquities gallery. After Hicham and Ali Aboutaam, the dapper Lebanese brothers who owned the gallery, pulled off the cloth to reveal the Apollo Sauroktonos, as it is also known, it did not take long for the museum to buy it.

It did so despite the Aboutaams’ disclosure that the statue’s ownership history was dubious at best.

Although it is thought to be the very statue described by Pliny the Elder in the first century, other details have been lost to time, along with one arm. The statue was part of a private estate in the former East Germany, the Aboutaams said, before it was discovered in pieces in 1990. The family who reclaimed the estate after German reunification sold the work to an undisclosed Dutchman in 1994. That person sold the statue to another collector, who sold it to the Aboutaams in 2001 with the understanding that he would remain anonymous.

The museum’s own experts spent a year investigating the provenance. Physical evidence proved that the sculpture had been out of the ground for at least a century, so its sale did not violate international laws and treaties aimed at halting illicit trade in art and antiquities.

Nevertheless, last month, the Apollo’s murky past returned to haunt the Cleveland Museum of Art and the Aboutaams, who are among the world’s most powerful dealers of antiquities. The Louvre in Paris withdrew a request to borrow the statue from the Cleveland museum for an exhibition after the Greek government threatened a boycott. The Greek pressure on the Louvre drew applause from many in the art world, particularly academics who have long criticized antiquities trading as fraught with corruption.

Hicham Aboutaam, 39, called the Louvre’s decision unfortunate: “The Apollo was proven to have been in circulation more than 100 years ago. The Greeks are not saying that the Apollo shouldn’t be here or that it was stolen. It is just their way of scoring a P.R. coup.”

The Louvre’s sudden case of cold feet was hardly surprising. Some of the world’s most prestigious museums have been sullied by accusations of acquiring artwork that was believed to have once been looted or stolen. The J. Paul Getty Museum of Art in Los Angeles agreed to return to Italy nearly two dozen artworks whose provenance was in dispute, and the Metropolitan Museum of Art in New York returned to Italy the Euphronios krater, a 2,500-year-old vessel for mixing water and wine that the Italian government said had been looted by tomb raiders.

As the provenance of antiquities and artworks is questioned, so is the provenance of dealers themselves.

The new wariness of collectors, both public and private, to buy or exhibit works that do not have the most rigorously documented history jeopardizes the business of even the most established dealers. So the Aboutaams are remaking themselves and their business. In a trade that has been full of grave robbers and forgers adding patina to new objects, they are busy digging up documentation for everything they sell in an effort to polish their reputation.