Collectors buying through dealers assume the piece is legitimate, and most of the time, that's true. Still, buyers should conduct their own due diligence to ensure they're not purchasing something questionable.

Here are some things buyers can do at the point of sale:

• Obtain a certificate of authenticity: If the piece is by an artist who is still alive, obtain a certificate of authenticity from that artist.
• Check the Art Loss Register: Collectors can check their potential purchase against the registry, which is an international database of lost and stolen artwork. Most legitimate dealers and auction houses will cross-reference any purchases with the Register. The registry typically houses an image of the piece along with a full description and, potentially, which collection it was in.
• Work backward: Collectors can track the piece's history, including the last owners and where it was shown or has appeared. That makes it easier to see how the organization acquired the piece.
• Evaluate auction records to determine prior ownership and dates of sale: Collectors should request auction records and sale records, making note of dates and locations. Once objects are stolen, they'll be sold via the black market, or they'll exchange hands several times until some unknowing buyer purchases it.
• Search the artist's foundation: Collectors can locate information on art by deceased artists through various foundations dedicated to that particular artist's work. Foundations can also connect collectors to renowned experts in that artist's work, who can then authenticate the piece.
• Be aware of dates: Look for possible red-flag dates, including those around periods of war or political upheaval. For example, art sales during 1935 to 1945 could in fact be looted pieces obtained during World War II and may have forged documentation. In cases where the original owners were Holocaust victims, the pieces may never have been reported missing.
• Pay attention to the country of origin: If a country has gone through a civil war, military action or political strife, there is a greater possibility that looting of artwork has occurred during these times of limited government oversight of their cultural heritage sites. For example, Middle Eastern or Southeast Asian countries underwent upheaval, and many of their art treasures were looted. Looters were known to break statues into smaller pieces and sell them off separately.
• Look for cultural patrimony laws: Many countries will have cultural patrimony laws, which means objects of historical significance are not allowed to leave the country. For instance, the Metropolitan Museum of Art recently discovered and returned to the Cambodian government some sculptures that were found to have been illegally removed from the country.
• Employ experts: Even with due diligence on the buyer's part, there is a chance that older pieces cannot be verified with 100-percent accuracy. With newer pieces, it's easier to confirm authenticity, but older pieces require the assistance of experts. When in doubt, hire an expert whose specialty is that of the artist who created the work. Experts can quickly determine the authenticity of a piece, and may be aware of any history of stolen pieces from that artist's collection.

Nowadays there are scientific methods to verify the authenticity of an item. Tests on pigments and fibers can determine the era in which a piece was created.

Recently, forensic testing has also helped collectors with authentication. For example, the estate of artist Ruth Kligman has been trying for years to authenticate a work purportedly by Jackson Pollack. A forensic investigation revealed a hair on the canvas that matched a polar bear rug that was known to be in Pollack's living room. Still, even with forensic testing, occasionally there will be disputes between the forensics team and the experts on that particular artist. That can create a gray area.

Instead, collectors should create their own paper trail. We encourage clients to keep a detailed record of their items, including the artist, title, medium, dimensions and any identifying marks or sale stickers on the back of the canvas, etc. If a work is stolen, having a detailed description of the item will help facilitate its recovery.

Even so, sometimes strong provenance does exist but it is denied by the artist. There was a case in the 1990s in which Balthus, a Polish-born painter who worked in France, disavowed a painting sold by a former wife. The case ended in court, where it was revealed the artist was lying out of retribution. The work was confirmed as authentic.