Were they new when you took them on loan? If so then no discount is due, 10% is more than generous. If they are ex demo and they have been in and out of cars and various houses, collecting bumps and scuffs, then 25% minimum. I bought some ex demo speakers, excellent condition, some light wear, at 25% off, and I currently have a UKP 2k pair that are well used and have a bashed corner for #300. Thank you Fanthorpe's Hull, nobody else wanted them as the price sank to #600 then #400. At #300 it was too good to miss.