Investigating wether manuscripts or inscriptions might by forgeries is a common taks in philology. There are a lot of them. "Good" forgeries use blank ancient p

Investigating wether manuscripts or inscriptions might by forgeries is a common taks in philology. There are a lot of them. "Good" forgeries use blank ancient papyros and even try to recreate ancient ink. So if the material looks authentic, it might neverthelss be a forgery. Therefore you look for mistakes of the forger. Perhaps the shape of a letter is too modern or too ancient, or a phrase, a word or a spelling does not fit. Or in the Qumran example: If you were sold a bunch of superficially very different manuscripts and then discover that they all agree in some subtle features, they are forgeries. A single such observation may raise doubts, but is usally (exceptions exist) not enough to be sure that a forgery is present. However, the more there are, the more certain one can be.