This topic is to include buying new, used, or trade equipment. Speaking for myself I seem to fall into what could be considered dangerous territory. Buying and selling in the search of the " Holy Grail ". I’m fairly sure there is no " Ah " in this hobby, and sit back and enjoy my final setup.
For instance, this month I bought and sold some Focal Utopias, Focal Clears bought and keeping ( for now ) Focal Clears, Wa6 SE bought ( jury still out on keeping these , Selling Gustard DAC-X20 PRO, Matrix Xsabre Pro to replace Gustard, Audeze LCD 2 selling. Thats all for now 
I must admit I don’t do this always, but when I get in the mood, its all out. The best lesson I have learned on these forums over the years is buy as much as possible used gear. I buy only new when I have to.
When I finally settle down with my buying frenzy, I finally settle into my best new flavor, only to change somewhere down the road. What’s your gear changing habits?
For my WA6, I eventually bought the upgraded tubes from Woo Audio as well as the improved power cord they recommended. Those things made a big, big difference…just FYI.
Welcome to the audiophile torment. I have about 30 headphones ranging from 50-600 bucks. Plus several, IEMs, portable amps, two mp3 players , 2 tubes amps etc… LOL
Oh Boy! Loads of fun. 
My main rig changes very slowly - mostly because it’s pretty much my dream-rig already. To get to that point, I did do a total reset on the source, DAC, amps and cables at the end of last year/start of this one. But other than possibly switching some tubes around when the new production WE300B start shipping, the only change I envisage there anytime soon is adding a Chord M-Scaler ahead of my DAC.
Headphones get added/sold all the time. I generally keep the flagship models, and a few well known references (e.g. HD6XX etc.) and then most of the other cans I buy are mostly to get an understanding of their sound, value, where they sit in overall performance (and to review) - and once that’s done they get sold.
So, for example, my pending pair of HD820 are likely to be kept. My incoming pair of TR-X00 are likely to be sold after a month or so.
Otherwise I tend to churn through a ton of gear … a lot of which I just buy to experiment with (buying used where possible) and for review/comparison purposes, and then sell - never having had any intention of keeping it. Though if I can borrow said gear, I’ll do that in preference to buying it.
Sometimes I’m surprised … the Phonitor x I was just intending to listen to and review. I wound up buying one and adding a proper solid-state amplifier option back to my main rig. And I haven’t let go of any of the Massdrop x amps so far (LCX, MCTH, EC ZDT Jr)
I find a certain charm to, and enthusiasm for, well performing basic, affordable gear, that I do with the TOTL stuff (which tends to just be setup and used to musical enjoyment).
I fall into the two dangerous camps of the early adapter and the serial upgrader. Buying used whenever possible makes me feel financially responsible yet I can’t help but notice that, even after online sales of a lot my discarded equipment, I’m still looking at a litany of cans, IEM’s, amps, upgrade cables etc. on my storage racks. Is there a Betty Ford Audio Addiction Clinic?
I have sworn NO REALLY I SWEAR IT that I will not buy any new headphone equipment for at least 6 months of which I am over a month into. (this prohibition does not apply to my home stereo, theater setup, speakers etc. … I’m only human after all)
Genetics has gifted and cursed me with exceptional hearing and launched my since-teenage quest to find perfect sound. 40 years later I’m still searching yet I’m a whole lot closer while acknowledging the last legs of the journey will be incredibly difficult and the laws of diminishing returns are cruelly impacting trip.
So how often do I change headphone gear? Umm none this month if I can just stay strong.
I love this term. Never heard it put that way, but I am definitely one.
As a heavy headphone/IEM user with specific listening constraints (e.g., metros, airplanes, offices, home, etc.), I buy whatever is most practical for each job.
My mobile units often die due to simple wear and tear and are used in less-than-ideal circumstances, so they have moderate quality (e.g., Sony noise canceling headphones). I buy something new for mobile use about once a year.
For home, I’ve tried to reach the point of diminishing returns/placebo effects for my sources. As my tastes run all over the map and lean toward exploration and uniqueness, most sources are never ever ever going to be audiophile grade. And most will be forgotten before long. I’ve recently purchased many things, but have also gone several years between changes too.
In sum, I buy when there is a realistic chance of improving the quality or listening experience for each type of use.