Among US collectors of the early 1900s, Berenson was regarded as the pre-eminent authority on Renaissance art. Early in his career, Berenson developed his own unique method of connoisseurship by combining the comparative examination techniques of Giovanni Morelli with the aesthetic idea put forth by John Addington Symonds that something of an artist's personality could be detected through his works of art. While his approach remained controversial among European art historians and connoisseurs, he played a pivotal role as an advisor to several important American art collectors, such as Isabella Stewart Gardner, who needed help in navigating the complex and treacherous market of newly fashionable Renaissance art. Berenson's expertise eventually became so well regarded that his verdict of authorship could either increase or decrease a painting's value dramatically. In this respect Berenson's influence was enormous, while his 5% commission made him a wealthy man. (According to Charles Hope, he "had a financial interest in many works...an arrangement that Berenson chose to keep private." )