1) Application for which the Inverter is required: The buyer needs to understand clearly the application and sizing. Also the changeover time that it can tolerate.
2) Power quality at the site: The power quality at the site needs to be studied, and proper site power quality audit needs to be done for proper sizing of the Inverter and back up.
3) Study the load: Proper study of the load needs to be done with a power analyser to understand the Power Factor and other parameters of the load to be connected.
4) Efficiency of the Inverter: Choose an Inverter that has a higher efficiency as it will provide a better RoI (Return on Investment).
5) Vendor Background: The vendor should be able to offer a solution, and not just a product. They should also have the wherewithal to do a proper site and load study.
6) Service Network:Size of the Service network, reputation on TAT and response of the vendor or company is to be studied.