Mathew/Murali,
One way to check for double registration / adverse possession is to do some of the steps in land purchase in reverse. By this what i mean is that usually, land survey by village official is left to be done as the last thing after property is purchased and registration done. But when you go to do the survey all the people with claims with start coming out of the woodwork and defeat your aspirations and you money will be gone, goodbye.
So when you are really interested in the piece of land, first negotiate with owner abut rates and other terms, then out of your own pocket shell out money and get survey done. All that the potential seller has to do is sign the application form, which if he is really genuine, he shouldn’t have a problem with. Survey rates are very nominal, but you have to pay “under-the-table” to get the village official to process your application and bring it to top-of-the-list. Survey official will publish official notice that he is going to survey the land piece on so-and-so day and all interested parties should be present for their claims. So when official survey is done, then all the first/previous purchasers, loan givers, malicious fellows, gossip mongerels, etc will start coming out and make protests/complaints/information. If nobody but you and seller turns up, then 90-95% chance that no problem likely to exist.
Of course, this is not fool-proof method, but for a few thousand rupees, you can save lakhs on getting cheated. My friend in Mumbai does this way only. If he is interested, he first negotaites informally, then asks for survey to be done and then only any other step.
Pls be careful in buying land. Farmers are not pure innocent creatures, but like all of us, interested in their own welfare first and the rest be dammed.