I think given this original_price/used_price value, then we could use some of our brains and think about things like the age of the speaker, the brand of the speaker, and the price range of the speakers.
We must assume that the consumer is somewhat intelligent, even though at times we see so much stupidity in the world. If we dont assume that the consumer is intelligent, then we would conclude that a free market would fail, and it doesnt.
Notice I used the word "Best" in the title... I even UCased it... Why? Because this is a word that encompasses opinion, desires, prestige, marketing etc.
As we all must conclude, that every consumer will listen to any speaker and come away with a different opinion of the experiance. Some consumers just have to look at the speaker to buy it, while others have to take them out for a short spin. Others study the speakers, read reviews, and listen for hours.
All of these people are valid in judging overall quality of a speaker.
Notice I said quality, and not SOUND quality. See, we audioholics are extremists. We will do ANYTHING for great sound, and usually spend lots of money and time listening to speakers. We dont care about how much space our speakers take up... hell we can always move the coach, or sit on the floor... We spend hours covering our walls with FOAM so that we may listen to them a bit better. We take out morgages on our homes for our speakers. We do all sorts of things that other people would find INSANE!
Yet this is our idea of quality... Is it invalid that a person may judge quality as if they dont see their speakers EVEN if he is ignorant to the fact that he is loosing huge portions of sound... Or is the opinion of QUALITY that of brand loyalty, or band name purchasing invalid?
Everyone has a idea of Quality, and by studing these ratio's we can use these to make better purchases. Just like stock prices, I am looking for the under priced over valued speakers and electronics in my price range.
If I could find a GREAT 20 year amp, that is cheap and extremely powerfull and great sounding for under a few hundred... I would jump on it without a second thought. But I look at ebays used audio equipment; I get LOST, in a see of products from years past. I have no idea of value, and have no way to judge or even start to look for a good purchase.
Ofcourse if I see Mcintosh for $20, and they work (or dont) Im going to buy them so fast your head will spin. But outside that, things get dicy.
Notice I always give recommendations of speakers between $500-$1000 on this site. This is where I know my stuff, and Ive studied most speakers in this range. I dont talk about more expensive speakers, cause I havent spent time listening to tons of them. I dont waste salesmens time If I am not going to buy something.
All this concludes that the book value of used speakers, when compaired to its original price, and a understanding of what value added it provides can produce results that would make recommending speakers to people easier. This would make speakers and sound equipment a commodity, that can be traded and explained. Dealers could seek out stocks of used equipment because of some knowledge that they a higher value then the set price. We as consumers would ultimately win, with knowledge of the best used items availalbe based on a price/value rating.