From p. 214 of the review by N. Na'aman of N.S. Fox, In the Service of the King. Officialdom in Ancient Israel and Judah, Cincinnati 2000, in Zion 67 (2002), pp. 213-218 [Hebrew]. The following section was translated by C. Edenburg, who apologizes if any misrepresentation has resulted.
"Fox discusses the epigraphic sources, and rightly emphasizes the grave dangers involved in depending upon materials found in the antiquities market. It should be stressed that a large part of the epigraphic findings surfaced first on the market, and it is extremely difficult to validate the authenticity of such articles. Anyone who has participated in excavations and knows how few epigraphic finds are uncovered during them, cannot help but being amazed at the endless number of findings which derive from unknown sources, and wonder what at the magic touch of antiquities robbers and dealers, into whose hands epigraphic finds fall repeatedly. It seems to me that only in a few cases, when the forgers were not adequately adept, have scholars succeeded in uncovering the forgery, but it is doubtful whether this is always possible. The antiquities market is very profitable, therefore skilled people have learned the 'secrets of the trade', and they can churn out articles whose recent provenance cannot be proven. I shall point to one example to illustrate how implausible is the picture arising from the findings amassed by now, but one could add many more cases. According to N. Avigad and B. Sass, Corpus of West-Semitic Stamp Seals published recently (1997), the number of seals and sealings identified as Hebrew is drastically greater (711) than the number of items identified as Aramaic (107), Ammonite (149), Moabite (59) or Phoenician (38). Even if we add to this number a few dozen Aramaic cylinder seals, the ratio of Hebrew items to all the others still remains unfathomable. However, we may find a self-evident solution to this puzzle, if we consider that the origin of most of the seals and sealings is on the antiquities market. "Due to these doubts, Fox decided to refrain from discussion of unprovenanced epigraphic sources. She mentions them in footnotes, but refrains from using them as a basis for any of her conclusions. In this, her approach differs from that of Y. Avishur and M. Helzer (Issues in Royal Administration in Israel according to Pre-exilic Epigraphic Sources, Jerusalem 1996 [Hebrew]), who relied heavily on materials originating on the antiquities market. Fox's cautious approach on this sensitive issue is commendable, and it supplies a stronger documentary foundation for her study than that employed by the other studies published so far."
Interesting. I recall that Robert Deutsch took us in detail through his authentication procedure for the bullae he was discussing, so the people working with this material are not unaware of the problem. This issue is, of course, quite relevant for the "James Ossuary" at the moment and it even arises for the Dead Sea Scrolls (which, of course, were mostly recovered by the Bedouin, not archaeologists). There is, for example, some doubt of the provenance of 4QGenesisb, which I published in DJD 12. It is supposed to come from Cave 4, but we weren't able to locate any fragments of it among the bits excavated from the cave, and its script and text leaves open the possibility that it actually came from one of the finds of texts from the period of the Bar Kokhba revolt. Likewise, some documentary texts originally assigned to Cave 4 now seem actually to have come from Bar-Kokhba-era finds. But in these cases the issue is provenance and date, not authenticity.