Buying second-hand RAM should be as simple as getting an email.
Every morning a system goes through Wallapop and Kleinanzeigen, keeps the newly listed memory modules, used or brand new, that fit what you are looking for —DDR4 or DDR5, desktop, laptop or server: UDIMM, SODIMM, RDIMM, LRDIMM— and emails them to you, ranked and explained: what others ask for the same module, how much you pay per GB and whether it works in your motherboard. And below, what happened in memory: DRAM prices, launches, reviews. No accounts, no app. Just email.
Write to
Which memory you are after ("2×16 GB of DDR4-3200", "64 GB of DDR5 for a laptop", "32 GB RDIMMs for a server"), or your motherboard and what it needs ("a B550 Tomahawk, one 32 GB module short"), or the part numbers of the modules you already have, to fill the free slots with the same ones (CMK32GX4M2E3200C16, M393A4K40DB3-CWE); your budget (per module, or in €/GB), where you live or whether you want it shipped, and what you won't do without: invoice, warranty or proof it's been tested. If you just want to keep up, say so: "news only".
What you get
One email a day with the new listings that fit best, and a weekly roundup on Sunday. Each with its price, brand and model, its capacity and how many modules it comes with, its type (DDR4 or DDR5; UDIMM, SODIMM, RDIMM or LRDIMM), its speed and CAS latency, and whether it is ECC; where it is and whether it ships, and why it is on top: below what others ask for the same module, the day's best price per GB, new or sealed, with invoice or warranty, the same part number you already have, or a price drop. And what doesn't add up, flagged: pricier than other listings, too cheap to be true, a lot bigger than what you need, or one that won't work in your motherboard (an RDIMM in a desktop board, DDR5 where DDR4 goes).
Whole PCs and laptops, motherboards with the memory fitted and DDR3 or older modules (unless you ask for them) don't make it; broken modules neither; the same kit listed twice arrives once; and what you've seen doesn't come back, unless it gets cheaper. The news comes in your language or in English, and the same story told by several sites, once.