Section 393(2) of the Income-tax Act places the withholding obligation on the buyer, not the seller, whenever the seller is a non-resident. In practice this means: when you sell Indian property as an NRI, the buyer is legally required to deduct TDS before paying you, and hand that amount over to the tax department directly.
The detail that surprises most sellers
Unlike TDS on a resident seller (typically withheld on the sale value under a different, lower-rate provision), Section 393(2) TDS on an NRI seller is calculated on the full sale consideration by default — not on the capital gain. For a property that's appreciated significantly, that produces a TDS figure that can be far larger than the seller's actual tax liability on the gain, simply because the default withholding basis ignores the seller's cost.
Where the rate comes from
The applicable rate depends on whether the gain is long-term or short-term, plus applicable surcharge and cess — or a different, often lower, rate if the seller has obtained a lower/nil TDS certificate under Section 197 in advance. Buyers who skip or underwithhold this TDS can themselves face penalties and interest, which is part of why buyers tend to withhold conservatively (i.e., on the full consideration) absent that certificate.
The Section 393(2) TDS estimator on the Real Estate Capital Gains page estimates the withholding a buyer would apply on a given sale, with or without a certified lower rate, so you can see the gap between what gets withheld and what you may actually owe.