Pay inflated price for used part replacement sold as new

I have a Central Vacuum System installed that needed repairs. There is only on service agent in the Western Cape. Motherboard was damaged ( suspected because of loadshedding). Agent came around and charged bearly R2k to fix ( using a second hand motherboard from a broken unit in his car). Insisted that it is new! Call out fee juat short of R1k. I argued that the part was definately not new, so I did eventually get a small reduction, but at the cost of reducing the warenty by a year ( as apposed to 2 years). Do your homework