What is considered a "standard" percentage of devaluation per year foor high end speakers?

Four years ago I purchased a like new pair of Revel M106 for $1250.   Listed them on Craig’s for $1100,  sold for $1000.  Buyer was happy,  I was happy to get $1k, effectively “renting” them for $250.  

I bought my my amps for half of new at only 13 months old.  Unlikely I’ll sell those anytime soon but they will be worth close to what I paid for a few years if I ever did. 

I like buying used if it functions like it should but it has to be super clean or I’ll pass.  Like anything condition and demand dictate resale value.  

Buy good vintage gear and you can enjoy appreciation, not depreciation.

At least 50%  on most speakers if sold on Audiogon
Dealer lucky to get 40% .  Wilson a, B&W and a few other hold value well or if Hot with several great reviews . Rule of thumb sell if possible a few weeks after a nice review ,and link to the ad.
I have sold nodded speakers night and day better then stock 
But most Audiophiles know little about Xover builds ,just parts name  you get little extra back for your efforts.

To roberjerman:   DCM Time Windows are/ were a terrific speaker for their time in 80's.  I sold them in mid-to high end store in Pennsylvania. The shape of their cabinet is still being duplicated today by many manufacturers.