As a concerned trader in roleplay it would ruin me, if i'm on a run to Dortmund with full cargoload of "Poisened Trash" or "Scrap metal", when i will be taxed for 500K and above. The height of the demanded tax should also depend to the cargoload.
Pirates should be interested to let the traders grow and not to ruin them, because they will have bigger ships one day so they can ask for a higher tax.