Verify that your object is actually a netsuke by finding the two small holes where the obi would be tucked. These holes will be about the size of shoelace holes. If your object does not have holes, it is not a true netsuke.
Inspect your netsuke for clues about it's creation date. The oldest netsuke, which originated in the 14th century, were made of wood and were purely utilitarian. In the early age of netsuke, from the 17th through early 19th centuries, the Japanese were influenced by Chinese art and culture, and produced netsuke portraying Chinese mythology and customs. Most of these pieces are unsigned. In the middle period, spanning most of the 19th century, artists carved Japanese-themed figures. These pieces tend to be of higher quality, and are more likely to be signed. If your piece is from the late 19th or early 20th century, it is likely to be of lower quality, since netsuke were not being used practically at this time. These pieces were influenced by Western values and culture.
The different types of netsuke are ichiraku, which has a basketwork design; kagamibuta, a bowl-shaped design with a metal lid; katabori, miniature sculpted figures and the most common type; kurawa, netsuke, which doubled as ashtrays; manju, with a circular, button-shaped design; and sashi, rod-shaped toggles often shaped like an insect or a twig.
The most valuable netsuke are finely carved with rounded corners and good coloration, and are signed. Some of the better-known artists are Mitsuhiro, Masakazu, Kokusai and Kaigyokusai.