How to prove that the bootloader of a device is unlockable when it currently shows as locked?

A newly bought Pixel device from a random seller can switch between carriers but the bootloader shows as locked. Are all pixel devices’ bootloaders locked by default? And how to show that it is possible to unlock the bootloader? And how to re-lock it for Pixel 2 XL. Any sources would be appreciated.

This phone is model G011C.