I'm buying instead of selling if I have spare cash.
And if i see cheap hardware (like 12 vega 56's reference) for 175 euro each. motherboard for 20 euro or less, rig frames for 14 euro etc etc. I'm buying all that **** up!
100 risers with cables for 100 euro, c'mon, they are just giving it away!
(been scammed once though, but luckily was only 72 euro)
I checked and in my area the Vega's or the 1080Ti are still expensive and hold their value very well. The only cheap GPUs which I can buy tons of are the RX 470/570, those are even dirt cheap on eBay. The pricing is pretty bad for the RX 470 because I've sold my even older Radeon 7970/280X for almost the same price. No idea why people are paying the same for a 280X than a RX 470.
Motherboards, especially Intel and their CPUs will never be cheap. The only cheap motherboards out there are those China brand ones and the only cheap CPUs you will find are the Celerons. Even AMD seems to be holding their values, unless you are looking at a Sempron.
Rig frames, you can usually just buy the hardware and cut it to your own specifications and build it yourself. In my area, very rarely is someone selling a used rig frame.