Comment by MostlyStable
7 hours ago
I've heard it claimed that the era of being able to do this (buy slightly old used server hardware cheap on ebay) is coming to an end because, in the quest for ever more efficiency, the latest server hardware is no longer compatible with off-the-shelf power supplies etc. (there was more but that's the part that I remember) and therefore won't have any value on the second hand market.
I hope it was wrong, but it seems at least plausible to me. I'm sure that probably fixes could be made for all these issues, but the reason the current paradigm works is that, other than the motherboard and CPU, everything else you need is standard, consumer grade equipment which is therefore cheap. If you need to start buying custom (new) power supplies etc. to go along, then the price may not make as much sense anymore.
When boxes get decommissioned it's generally the entire thing. So you can pick up used power supplies as well. Or just buy new because even if it isn't ATX it's still a widely produced item that's used across multiple product lines.
The troublesome hardware is the stuff with custom backplanes and multiple daughterboards each hosting a node. Also AMD CPUs that lock themselves to a single motherboard.
The power supply incompatibility came to fruition a long time ago. Buying used Supermicro ATX motherboards to build into servers stopped being a thing for me about 1 decade ago. But used servers and desktops, even with their non-standard parts, have continued to deliver high value for me even today.