In case you are a seller with a GST number and also have an IEC code, then you will be charged by the above duty table, like the 20% customs duty, but you have to Import in large quantities, like 5 or more units. Otherwise, the same 42% duty is applicable.But for selling purpose what duty to pay
Also, you have to visit before the customs superintendent's office with your documents and invoices where your parcel is landing on the same Day (e.g., Mumbai foreign post office) to avoid overcharging customs duty; sometimes they miscalculate value of the parcel.
If you miss above step then you have to pay whatever customs duty they are charging once your customs duty is calculated then there will be no option left for you other then payment.