Google apparently sent Verizon locked Pixel 3 to some who ordered the unlocked model
As most phone enthusiasts know, to customize an Android phone and flash custom ROMs onto the device, the unit's bootloader must be unlocked. The bootloader is the code that is executed before an operating system starts running on a handset. The unlocked version of the Google Pixel 3 and Pixel 3 XL, available from the online Google Store, is supposed to allow users to unlock the bootloader. The Verizon branded version of the phones come with a bootloader that will remain locked, preventing the user from customizing his handset.
Pixel 3 or Pixel 3 XL from the Google Store just to make sure that the bootloader on the handset they receive can be unlocked. However, as seen on Google's Issue Tracker site (via Droid-Life), some Google Store customers are finding out that their new Pixels are arriving with a bootloader that can't be unlocked. When looking through the Developer Options menu on their new phone, the listing for OEM unlocking is greyed out.Those experienced in flashing custom ROMs on their Android phones would be expected to purchase an unlocked
Those who cannot unlock the bootloader on their new third-generation Pixels have apparently been sent the wrong version of the phone by mistake. A string of code found on these units indicates that they are actually the Verizon branded variant (ms-android-verizon) instead of the unlocked version (ms-android-google).