Passing on GST benefit required to reduce prices; charging higher post-GST instalments may attract anti-profiteering action. Builders must pass on the GST-related reduction in tax burden to buyers by reducing prices or instalments and must not charge higher tax on instalments payable after GST implementation; withholding such benefit or charging higher post-GST rates may be treated as anti-profiteering under Section 171 of the GST law.