I wouldn’t buy a used MacBook from an individual seller unless I could meet in person to verify there’s no BIOS/TPM lock going on that would prevent me from doing a secure erase and wiping the SSD to start fresh. A laptop with a replaceable ssd is probably less of an issue, but I’d still feel more comfortable having a picture of the BIOS showing no password set or anything, and a picture of it booted to desktop at minimum so you know it isn’t a stolen laptop that has a password no one knows. If you’re buying from like a second hand recycler or something, anyone that sells through significant volume of devices, I’d be much more comfortable just pulling the trigger sight unseen.