I have a friend who recently bought a high end used trumpet in perfect condition. It was new at least 10 years ago, maybe more, but the current value has actually decreased. What would cause a brass instrument in pristene condition to lose value, although it was slight?

old things can sometimes just break down. like a perfect30 year old flute my friend`s sister got from her mom. it played well for 3 more years and then started to fail