Authenticity is the prime factor affecting the market value of a work of art. String instruments are among the most valued works of art, particularly those made by the old violin-making masters of northern Italy in the late 17th and early 18th centuries. However, it is difficult to verify the authenticity of string instruments on the basis of style and design alone, as these are often copied or forged. Uncertainties related to craftsmanship can lead to financial and legal controversy, sometimes with even millions of dollars at stake. The authenticity of the Stradivari "Messiah" has long been disputed. Controversies at the end of the 1990s concerning its craftsmanship have enhanced interest in dating this violin. After different dendrochronological analyses provided conflicting tree-ring dates for the front of the violin, a scientifically-sound dendrochronological study eventually established 1682 as terminus post quem, i.e., the year when the last ring of the violin front was formed, before which the violin could not have been made. This date is consistent with the attributed date of manufacture, 1716, supporting Antonio Stradivari as the maker of the "Messiah". However, this controversial dating of the "Messiah" sent shockwaves through the violin community. Here, we present the main facts which played a role in this controversy and we show how dangerous the use of dendrochronology can be if investigators do not adhere to well-established techniques and are not versed scholars in the literature. Such controversies threaten the reputation of dendrochronology. Today, many false theories and conceptual mistakes continue to circulate in the violin community. A thorough and scientifically-sound dendrochronological analysis of the wood used to make the instrument is the only analysis that can objectively indicate, if not the exact year an instrument was made, at least the date before which it certainly was not made. Here, we describe the importance, in terms of acoustics, of the anatomical characteristics of the wood with which instruments are made and its possible geographical provenance. We review the dendrochronological studies undertaken to assess the authenticity of the instruments made by the old Italian masters. Such studies help to establish the earliest date the tree from which the wood was taken could have been felled, and to determine the source region of the wood. We present the main achievements and challenges that have arisen in the past 50 years of studying the authenticity of string instruments, and discuss the limitations and advantages of using dendrochronological methods to establish the provenance and time period in which a work of art was created. Finally, we describe needs of research in history, wood anatomy and dendrochronology, proposing several new methods that may open up new avenues of research and aid in the assessment of the authenticity of old string instruments.