Trezors come only with the bootloader pre-installed, the firmware is installed when first initializing the device making sure one can start from a clean slate.
Presumably the Trezor clones use the same bootloader, allowing it to install and run the official firmware. If that's the case no warning will be shown on the web interface.
Problem being that while the software may be verified, you have no way of knowing whether the hardware is trustworthy. They could have used less secure components, they could have installed a backdoor on the hardware level, etc.
Actually then there is no way to determine if it is an original or a copy of Trezor hardware wallet, maybe only if user have 100% original Trezor ordered from the manufacturer directly and suspicious product in front of you.
Apart from the difference in holographic seal there are probably some differences in the box and in the hardware wallet itself. Some tips can be seen in this
video, but only right way to buy hardware wallet is directly from manufacturer - in this way the possibility to get fake wallet is maximally reduced.