How much are Shan Guolin's calligraphy and painting works? How to identify them and how much are they worth?

Dan Guolin (1942.2 ——) was born in Xiaoshan, Zhejiang. He is good at studying the theoretical history of China's calligraphy and painting. 1965 graduated from the art history department of the Central Academy of Fine Arts. He has served as a member of the exhibition department of Shanghai Museum, deputy director, associate researcher and researcher of the painting and calligraphy research department. Editor-in-chief: Shu Hua Collection of Paintings, Collection of Works by Famous Maritime Artists, etc. He has published papers such as The Track of Zhejiang Military Year and Its Painting Style, A Preliminary Study on the Trading Mode of Literati's Calligraphy and Painting in Ming Dynasty, An Analysis of Zhang Daqian's Ink-splashing Landscape Paintings, and On Modern Scholars' Painting. He has given lectures in the United States and participated in international academic seminars in the United States, Japan and Hong Kong. His calligraphy has also been hyped to about 30,000-50,000 square feet.