I've bought about a dozen from friends and family.
Search on eBay.
Find a seller with many of the same model. These are tech contractors offloading the laptops they just replaced under some contract - you'll get a laptop that's been sitting in some managers drawer for the last 3 years.
Next go to the contractors own website, not ebay. See what stuff they have.
I usually email them and just try to express interest in buying 2 or more laptops, ask what peripherals they have - get a dock or something. Ask about RAM or SSD upgrades, things like that.
You're helping them offload their second hand stuff, avoid ebay fees, not being a dick.