I am currently using a Dell Optiplex 3000 while my sister has the Optiplex 3080, both acquired at about the same time.
Mine has the Intel 12th gen i5-12600T while hers has the Intel 10th gen i5-10500T, both with 2x8GB RAM now.
Same price range of about 16.5k as mine is higher spec'd while hers was supposed to be brand new (kuno).
Mine came with 1x16GB but I changed it to enable dual channel mode. Hers came with 1x8GB with another 8GB added.
Both has the 256GB M.2 2230 boot drive but I added a WD 1TB HDD. I added in her original SanDisk 240GB SATA SSD.
CPU can still be upgraded to Core i7 but it's quite tricky to maintain the internal temperature due to the cramped space.
Mine is connected to a 34" widescreen monitor (3440x1440) and can drive it up to its maximum 144Hz refresh rate.

I initially built myself an AMD Ryzen gaming rig with at least 7 fans including those for CPU and GPU.
But I barely game nowadays and it's mostly being used for browsing, streaming and/or word processing.
So I decided to kinda 'downgrade' to something that would just fit said requirements.
I also have a laptop but although the CPU is still very much capable, the built-in 8GB non-upgradeable memory limits it.
It can get saturated when I have multiple browsers and tabs open, causing it to pause/freeze or slow to a crawl.
Images are of a 3070, 7000 & 7090 but the 3000 & 7000 series MFF PC layout is just about the same.
Differences may vary even within the same series. Some has the 2.5" SSD/HDD expansion slot while others are M.2.
The 3000 has a single universal 3.5" audio out, while others have individual line out and headphone out ports.
The number of DisplayPort, HDMI port, USB2.0/ USB3.0/ USB-C port varies also as BT and Wi-Fi availability.
The 7000 series can go up to Core i9 although I haven't seen one being offered locally in the 2nd hand market.
And yes, I do believe most of them came from BPOs and POGOs who may have closed down already.
There are those who do both bulk and retail, while others buy from them and resell it in the markeplace.
I think these are value for money as just the CPU, RAM and SSD already make up the cost for the offered price.