I have never had this happen to me thankfully but I absolutely go out of my way to make sure the device is unlocked before I ever lay hands on it and if it's not for some reason I will absolutely return it because I flash lineage as soon as I get a new device. What I've found myself doing is buying new mid-range phones instead of used high-end devices. So I often find myself with like OnePlus Nord or Moto G or Pixel A or something like that.