Presumptive taxation: opting out triggers five year ineligibility and requires books and tax audit consequences. Presumptive taxation carries a binding five year adherence obligation; opting out in any subsequent year renders the assessee ineligible for the presumptive regime for the next five assessment years. From the assessment year of exit the assessee must keep and maintain books of account and, if total income exceeds the basic exemption limit, is subject to the statutory tax audit obligation.