First and foremost understand which Snatoor suits you best – Indian, Chinese, Persian, or any other. Once you understand then dig deeper into the features of the one you are planning to buy. Collect info; ask questions, visit shops, websites and so on. Its all about understanding what you are paying for.
If you are buying the Santoor as used in Kashmiri classical music, The Kashmiri Santoor is more rectangular in shape than its counterparts and may have more strings than the original Persian counterpart, which generally has 72 strings. So ensure you have counted then and made sure they are not flawed in quality of positioning which will help it fine tune better and the final output of the sound will greatly depend on it.
Santoor is played with a pair of curved mallets made of walnut wood. Ensure the mallets are not flawed in anyway as they finally create the resultant melodies. Examine the sound chamber. It should be made of walnut wood and the bridges can be made of local wood and could be painted dark like ebony. Ensure the strings are made of steel.
People who are just setting out to buy Santoor should get advice and know tings like how to improve its sound. How to get better arrangement of bridges; whether buying a certain type of bridge would be better; also whether buying a certain quality of chords will make a difference and if yes, how, and finally they should check out where to buy a replacement for a broken accessories.
Finding answers to these questions will give them an insight into the instrument they are planning to own. It will also work as a reality check for the buyers and the information will equip them to make better buying decisions.