NRIs can earn rental income. It should be credited to the NRO account.
If rental income directly remitted to abroad then certificate by CA.
TDS @30% should be deducted and the deductor should have TAN No. and he should provide TDS certificate.
If the deductor does not deduct TDS then he is responsible for non deduction of TDS.
Rent will be taxed in the country in which the property is situated and due credit will be taken. For claiming refund of excess TDS, filing of Return of income is compulsory.