Do you buy gear new, used, both?

Mostly new here, but I have  bought used occasionally. 

Mostly new, although some of it quite old now.

My last big purchase, a turntable was second hand, although I did buy some new bits for it.

I keep my equipment for years.  So depends on the type of component (amplifier, preamp, DAC, etc). Generally, I would buy used where there are no moving parts, age (less than x years), condition is an 8 or better vs price (discount from new if current model). For items with moving parts (CD players, turntables, etc.) generally no, but have done so on a CD transport and a phono cartridge where I knew the seller.

For open-box (new or returns) - condition, seller (store or individual) and discount from new selling price would be determining factors for me.

Almost everything I own is used. My new components are a roon nucleus and a Sonos Port

Except for cartridge and a pair of RCA cables I have nothing new in my system. And a few pairs of NOS vintage tubes.