Margin scheme/profit margin taxation (second-hand goods)

[nilskm]

I can see that I asked this question over 10 years ago with no replies. Has anything changed in iDempiere since then to be able handle this kind of complicated taxing? I created a solution in ADempiere that kind of works but it doesn't feel great. When selling used products I add a second line where I put the revenue. Then in reports like the invoice I merge these two lines into one. But it gets kind of complicated when creating sales reports etc.

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Has anyone tried to handle "margin scheme" in iDempiere? 

Margin scheme is used within EU (and probably other countries to) when you deal with second-hand goods. The point is that you only pay tax for the part that is revenue to avoid double taxation. 

An example: 

I buy something for 900 € from a private person (not a legal entity / corporation)

I sell it for 1000 € (to a private person). 

The tax is then calculated on the revenue 1000 - 900 € = 100 € which I report to the government. 

I haven't been able to find an easy way to handle this in iDempiere.

First I thought of setting a specific tax category on the product with zero percent tax. Then use a model validator for MInvoice where taxlines was added. But I think that the revenue will be wrong then so I guess I'd have to add lines to accounting to. Since the revenue should be 100 € minus the tax. 

Second thought was to use a charge. Still zero percent tax on the product then use a model validator on MOrder or MInvoice and add the tax to be paid as a new line with a charge. 

Anyone has any thoughts on this issue? 

Best regards

Nils