Master ownership of Android devices

The problem you describe has nothing to do with FRP, it's more likely a problem devices get stolen and resold.

A reseller has to ensure that their devices are not managed before selling them if they don't or sell them even they are managed, they are not resellers to trust. And as a consumer, i would startup every such device online (using SIM or Wifi) until request of entering the google account is arrived and not pay before.

We had several cases where devices which got stolen and someone tried to re-enroll they all ignored all the messages saying "your device is not private" and so on and then wondering why the device is locked into a kiosk screen and not useable or if they are already shipped far away just ran into a useless mode even without FRP.

This doesn't prevent us from stolen devices but hopefully shows the thiefs at some point that it doesn't make sense to steal such devices and try to resell them online or on a flea market.