There's really only one answer to your dilemma. If it's for sale, offer it for sale. Place it where the greatest number of likely buyers will see it; provide the biggest, clearest, most accurate scan(s) you can; give the most detailed and accurate description you can - and sit back and wait.
The problem with specialisation is that it can go to almost infinite lengths. Once you pass beyond the Gibbons
Stamps of the World or equivalent level, there's no end to it.
Here's a concrete example of what I mean:

Now to start with, there are no specialised catalogues of Barwani. The best you can do is check the stamp in Gibbons' Part 1 or India catalogue. You might, if you were sufficiently desperate, and had enough Indian region material, join the India Study Circle, and trawl through the back issues of the Circle's journal for any additional scraps of information, or you might even chance upon the 30-odd year old series of articles I wrote on Barwani in the
Collectors Club Philatelist. But we'll assume, correctly, that these sources draw a blank on this item.
So you look at Gibbons. You identify the stamp as SG 33B. You look at the beginning of the Barwani listing, and see that Gibbons prices Barwani on cover at 'from x3'. So you start with catalogue value of £28 x3 = £84. However, the stamp is damaged, so deduct - how much? - say £24, assuming, rightly, that SG 33B is probably down at the x3 level, being relatively common.
Now, if you were much more of a specialist, you'd notice that the stamp was cancelled at Talwada Deb - and unless you had a very, very large collection of Barwani, this would be the first Talwada Deb cancellation you'd seen. Then, the card was sent to another village, Rajpur, not to Barwani Town; most Barwani covers went to or from Barwani Town.
Then you'd turn your attention to the stamp. It isn't just a 'Wide' setting: it's a Setting VI Wide setting. And finally, you'd identify the stamp as a cliché 2.
So the ultimate Barwani specialist might need precisely this stamp to complete the set of four clichés of SG 33B, from Setting VI, used from Talwada Deb ...
You can see how far it's possible to take this sort of thing.
If you'd wanted me to sit up, pay attention, and bid with my ears pinned back, you wouldn't need to tell me all of that. You
would need to provide enough of a pointer to get me to your lot in the first place and a sufficiently high resolution scan of the whole card, the postmarks and the stamp to know exactly what it was.
You'd then have to hope there was at least one other collector as obsessive as I am.