How many people here generally buy used?

Fortunately I worked in manufacturing, and I have made (I couldn't call it DIY as I was a professional)

Made new:

• Lenehan ML1
• Lenehan ML2
  
• balanced Ribbontech interconnects
• Ribbontech speaker wires
  
• Curious Cables silver USB cables.
  [the above I built, but none are my design, all are available to purchase from manufacturer].
  
• DIY subwoofer.
  

Purchased new:

• Geiseler M17D - Groß DAC
• components for my music server (Femto USB card, fanless case, fanless industrial mini ITX mainboard etc.)
• Plex 200W linear power supply
• Pro-Ject Pre Box RS (removed from system as it introduced noise).
  
• Two pairs of Lenehan speaker stands.
• Mad Scientist - Heretical Digital Cable
• Cambridge CXUHD 4K player (also used as a music server)
• Assorted springs for isolation
  

Purchased used:

• Furman power station
• Synergistic Research Master Coupler X2
• Datasat RA-2400 amplifier

Both, as with many here I imagine. Some great deals on used cables over the years, a couple of perfect REL subs for 200 bucks each, my Dennis Had amp was a couple of months old and around 400 bucks less than new, etc. A Linn Basik/Akito in near primo condition turned out to be a great thing, and although I look around for something to replace it from time to time it sounds so good it just stays. 

For me it's a case of the greater the number of moving parts the greater the need to buy new when it comes to audio. 

With speakers there's always the concern with surround rot and invisible damage to drivers (esp tweeters) and voice coils. I think piano at reasonably high volume is a good test for coil damage. You'll definitely know it when you hear it. A tremendously non musical screechy sound.

With amps there might be issues with calibration and imminent dry joints etc. My Creek Destiny amp I bought used soon developed issues with the pre/out bypass switch. Luckily I was able to bypass it with the use of jumper cables.

With the rest there's also the risk of various tweakery applied beforehand too. Frankly I'd rather buy a product as it was designed - not as a failed tweak job.

Having said that there was no other way of buying my current 1970s speakers than buying used. Thankfully the previous owner seemed to pay great respect in keeping it in original spec.

In any case it would always be good ethical practice to declare all mod history when selling. I had to when I sold my LP12.

Despite that the buyer couldn't seem to get it off my hands fast enough.

I prefer to rebuild/restore used gear that might have issues, especially turntables. Currently run a rebuilt Beogram, Nak tape deck and a rebuilt NAD preamp. All other gear is used as well except for a Sony CD deck that I got new way back in 1987.