I tried to import the taxes (as a way to have a better grip upon the import system.)
I noticed two points:
- If the "9" format is selected, the [Rate] field (which although it is an INTEGER, behaves as the Amount fields and is scaled by 100 in the database) is not scaled
- The import system check if the rate exceeds xx% (some high value, I guess 100% but I did not check exactly); however it silently accepts any value below 0,01%, something which is not possible through the GUI
- 0% is the correct rate to be applied when the operation is VAT-exempted (for example, U.E. sales, or U.K. VAT around 2017) which is a different case from being Not Subjected to taxation
- Negative rates may happen for some schemes of parafiscal taxes; for example here in Spain, when (some classes of) individuals send B2B invoices, there is a part (usually 15%) which is subtracted from the to-pay amount, which represents the part of provider's income tax withheld; later the customer will declare and pay that amount directly to IRS (a similar scheme applies in France, retenue à la source, under different rules.) The general way to transcribe this system here in Spain in invoicing systems is to add that withholding as a "parafiscal" tax.
- Also, one can easily find to use the (otherwise unused) parafiscal taxes to model some kind of general deduction to be applied on the invoice, for example for early payment
Is it possible to consider variation to this scheme? I do not have a good idea of the complexity this may add (Also, while I have heard of them, I never encountered actual cases when one has to use parafiscal taxes...)