For large-value transactions on which an indirect tax is levied (service tax, excise, VAT, octroi), taxpayers should be offered say, a 1-2% discount on the tax rate if they quote their PAN.
This can, of course, be made simpler—if a person pays by a debit or credit card (which being linked to a bank account is already linked to a PAN) or a bank account, s/he too should be given a “discount”. This will naturally incentivize documented payments, which can eventually be moved to electronic or mobile payments, making them easier to track.
As the flow of unaccounted money starts getting checked and a profile of assessees is built around the primary key of a PAN, it will more easily lead to the stock of black money. Incentivizing e-governance initiatives can help to make the adoption of the system quicker while helping to make it more transparent.