With so much happening on the AI/HPC hardware front lately, I wonder where the prior-generation servers end up once well-funded companies upgrade. I'm interested in acquiring a GPU-laden machine with enough VRAM for local fine tuning, training, and batch inference. I could build a workstation with current or older-gen GPUs, but it seems like a used professionally built rack-mount machine could be higher value.
I've gotten a handful of free equipment (no drives) by being willing to show up and take whatever is being offered. Likely craigslist is your best best unless you're willing to make some local connections.
They will not have a store front or advertise you'll just call the owner and ask if they have "X" or equivalent and if so you can go get it. I've used a few of them over the years for monitors and wyse terminals for small businesses.
ymmv!