When you are planning a scam by selling faked artifacts of any kind, you need a good explanation where you found them. Probably the simplest and thus most plausible explanation is a treasure trove in a cave. Although it is absolutely unlikely to store anything of worth in a damp cave, we've seen this so often in movies and read it in book, we just believe it.
The worlds most famous story of a cave treasure hoax took place in northern Spain. Don Marcelino Santiago Tomás Sanz de Sautuola (*1831-✝1888) visited a cave on his property called Altamira. His daughter looked up and saw paintings on the ceilings. They were so well done, the archaeological establishment judged the cave art to be a crude joke or a hoax. The discoverer was said to be a fraudster, because at the time of the discovery he had a guest who was painter. De Sautuola published his find between 1880 and 1882, but most of his opponents refused to even inspect the site. This destroyed his life and he died prematurely six years later, a broken and bitter man. Later archaeology evolved, and the professors who first laughed at Sautola apologized for their error. The most famous was the Frech Abbe Beuil, who publicly appologized, and once said that this was probably the biggest mistake he made as an archaeologis.
So is this a hoax? We believe not, but it teaches us that it is very hard to tell the difference. The basic thing is, to allow as many people as possible (without destroying the site) to see it first hand, to do scientific research, and to accept other ideas. As a result there may be a scientific proof of its authenticity or not. But without this examinations, there is a 99% chance it is a hoax.