A property seller in Delhi is facing an issue where the buyer is unwilling to provide their Aadhar and PAN card details, which are necessary for the seller's income tax filing to declare a capital loss. The seller is inquiring about their right to request these documents and what other proof they will receive post-registration. It's advised that the buyer must provide an Aadhar card during registration, and the seller should amicably request the PAN card for tax purposes. If the buyer refuses, the seller may consider withdrawing from the sale and finding a more cooperative buyer.