i dont know how you can feel insulted, just think for a minute, when you were sold the bike yu would have assumed he has made a profit,,,,,, eg about 20%, so take that at least off the bike , also for depreciation , then think if you were buying it second hand , what would you expect to pay , you would want a hefty discount from the new price otherwise what is the sense in buying it, the dealer then has to make a profit , again about 20% to cover holding costs , wages , power , security and he has to then warranty the used bike,
try trading in a car you wouldnt even get close to the percentage that you do on a bike, when i bought the 2011 convertible , at about $43,000 the dealer offered me $ 13000 on my softail custom with 100,000 km on it , i chose to keep it as the going price on a private sale would be around $17-18000 not bad for a 16 yo bike that in 1995 cost me $25000
try that with a car