Is it legal to buy and sell collectible notes in India?
Yes, as collectibles. They are not sold as money.
We sell banknotes and coins only as collectibles, for numismatic, historical and educational purposes, and not for use as legal tender. Dazzle Monk does not exchange foreign currency or transfer money, and is not a money services business.
In 2017 the Madhya Pradesh High Court (Indore bench, W.P. No. 4682/2015) dismissed a petition against selling notes with special serial numbers at a premium. It found that this trade is not prohibited by the Reserve Bank of India Act, 1934.
Laws differ between places, so buyers are responsible for checking the rules where they live.