I think i am what they call a "typical" consumer in the music space. To me, music is not an exact science - more of an art thing. I keep a couple of headphones and depending on the mood, I swap. For e.g. I could "feel" I want to enjoy like the punch of the HD650. Other days, I feel like having a light and easy listen - so i reach out for my ESW-10 jpns.
Then again there are just some days I feel a bit more "vocal" and i go and grab my PS1000....So i do keep a bunch of headphones and use them for what is the mood.
There are 2 things that I determine if I like the headphone/earphone.
1-Should i buy it?(aka first impressions or girlfriend mode)
2- Should i keep it?(aka marriage mode)
For 1-"should I buy it" (first impressions/girlfriend mode):
I would think that "hype" or herd "instinct" is pretty important in determining purchase- Usually this is where i check the forums on what headphone are good and what are not. (and that's what makes this forum really important). Because that is what happens before we get a chance to audition. See what the guys are saying - what's hot and what's not. Of course if there is a bunch of head-fiers saying "headphone X" is the ultimate headphone and has decimated all the previous headphones known to man- the incentive to try "headphone X" is great. And conversely, if "headphone z" is like yuck spit puke, then the incentive to try is much diminished.
Next comes the buying decision, which again is many factors.
1)The looks /Packaging - very important. what appeals to the eye. (like Adam reaching out for the forbidden fruit). It must look really tasty! On this point, I say the audio tech Japanese chaps are masters of packaging.
2) Price/Quality - not really saying go cheap. but i think value. if i am paying USD500 for a headphone, surely it must not sound marginally better than say a USD100 one. After playing around with a few headphones, I think I already have a "benchmark" for what I consider value (nothing to do with the DAC!) .
3) Mood- no point shopping when i just quarrelled with my wife or my boss gave me a hard day.
4) Faith - I often end up buying a headphone just for fun even though initially impressions did not impress me - just because some headphones take a longer time to burn in than others.
I did not like the PS1000 or the HD650 but after burning in, man, they are just night and day to me.
Then there is marriage mode:
I think headphones are the equivalent of shoes to women. After after trying them for awhile, you really know if you like them or not. For example, no matter how people say the IE8s were good, I just didn't find the sound to my "taste" so I tried them, didn't like them and the great thing I sold them to someone else who will like it.
That's my unscientific 2 cents worth