I initiated coverage of the Indian Convention States a while back by tipping Chamba Sc. #1-15. As I believe that this is one of the most undervalued areas in Indian Philately, I now continue to focus on it, by recommending the 1885-97 Overprinted Issue of Nabha (Scott #11-25). The top three values of the set (2r to 5r, Sc. # 22-24) had printings of only 572 each, and Scott '10 values the set unused at $ 352.35. While fake overprints may possibly exist on the high values, this does not represent much of a risk, because the difference in value between the stamps overprinted for Nabha and the basic stamps of British India are not enough to justify faking them.
Until the last decade or so, most of the demand for stamps of India's Convention and Feudatory States has come from British Commonwealth collectors and specialists outside of India. With India's economic rise, its stamp market has been heating up considerably. I am confident that in the coming years, the center of demand for these collecting areas will shift to India, as the number of stamp collectors there will number in the millions, if not tens of millions.