Is there an active market for used servers?

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 wonder where the prior-generation servers end up once well-funded companies upgrade

E-waste recyclers because they can handle bulk.

Suppose 500 servers get replaced. To a first approximation, nobody who needs 500 servers is interested in 500 old servers and if they were they already bought 500 servers or are waiting for a better deal or aren’t ready to move out their 500 servers to make room. Recyclers have the real estate to receive 500 servers and experience disposing 500 servers.

And there are not 500 hobbyists lined up…and who wants to deal with misinformed consumers? There are all sorts of incompatibility nuances with complex computer hardware.

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Advice: If your hobby is gonna be training models, just build a box. If you want a server rack hobby, then buy a server rack and be ready to pay the dumb tax.

My advice is to search for the stuff you want on eBay, then filter results for sellers near you, identify some interesting sellers and try to visit their facility in person. If you buy through eBay, then a less awkward tactic is to choose "Local Pickup" instead of a delivery service. When you're at the facility, ask if you can take a look around or if they know of other sellers for used server equipment.

Likely craigslist unless you're willing to make some local connections.

Be aware this equipment is not pleasant to be around (loud, hot)

Server hardware is too heavy/bulky to be able to support a big online marketplace. Your best bet is to identify the type of organizations that buy the server hardware you want to buy used and find out how they get rid of their excess.

I've gotten a handful of free server equipment (no drives) by being willing to show up and take whatever is being offered.

Check with your local non-profits, most 2nd hand no warranty/guarantee shops are in your local small industrial parks and sell mostly to non-profits or very small companies.

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.

I have made a trade with someone local, worked well for me: https://www.reddit.com/r/homelabsales/

ymmv!

eBay routinely has listings for desktops with 8th to 10th gen intel CPUs and quite a bit of beefy hardware for under $200 overall. Some of them also come with GPUs in them.