And I believe the NL tax reporting for large gifts also requires you to identify the donor.
In essence, the limitation is not on the method of payment but on the core activity, that any significant income from contracts, deals, trades, barters, transfers, gifts, settlements etc need to be non-anonymous in order to be legitimate, so if the method of payment does not identify the payer (i.e. cash) then simply it's your duty to identify who you're dealing with, from whom you are earning money.