I’ve run into that a couple times and it’s super frustrating because there’s 2 different types of “unlocked”, and they’re pretty much all carrier unlocked these days, where an AT&T SIM card will work in a Verizon branded device, but the Verizon ones for sure never allow OEM unlocking. If buying new from Google, I’ve always bought the “Unlocked” option. If buying used, I’ve given the seller instructions on how to check that the option is available. At least on Swappa, it’s been a pretty painless process.