Used part fitted while charged for new part

I got a quote from them for a new Landrover Discovery 3 V8 radiator. When dropping the vehicle off this morning it was confirmed that it is for a new radiator to be fitted. Upon collection this afternoon I noticed that the radiator is not new based on wear and tear markings. The staff insisted it is a new part and the more I pointed out marjs etc the more he insisted its new. He then offered me a 20% discount on the part price. I have taken pictures of the radiator as proof of the state of the part. NEVER TRUST THEM WITH YOUR VEHICLE. The charge new prices for used items