In order to buy a suitable instrument, we must first know the structure of the instrument. To get to know kamancheh, you can read this article and get enough information about the structure of kamancheh. In the next step, you should pay attention to the type of wood used in the instrument, the quality of the strings and the quality of the bridge (kharak).
At the same time, make sure that there are no structural cracks in the construction. To consider these things, you need the guidance of a kamancheh expert. You can ask for advice on buying a kamancheh instrument with experts in this section.