garmin 680 demo unit can it be formatted??

I would be surprised if it truly were a fully functional hardware device. There's a trade-off between the additional cost of manufacturing a demo-only version, the cost savings of eliminating unnecessary parts, and knowing that the demo version is sufficiently crippled to keep someone from stealing it and selling it as the full model.

The GPS receiver is unlikely to work in a metal-roof store, and the software is as you mention setup specifically for demo, so I would guess it is missing substantial portions of what's in the boxed units.

Key things that could be different:

• Lack of GPS chipset
• Use of ROM or smaller flash memory instead of the typical large flash
• Lack of an internal battery
• Lack of actual maps vs. select geographies, or even just well-designed screenshots
• Lack of USB interface

It could be that it shares only a shell and touchscreen with the real deal, perhaps just a glorified Flash animation player.

The only things that are referenced from the bit you can format are maps, POIs, vehicles, voices etc.. the firmware that the unit is running is only loaded when it detects that a newer version of it exists (usually in GUPDATE.GCD). I will bet, that the Demo firmware doesn't perform that check.

Try running Webupdater and see what it does...
...it may be necessary to edit GarminDevice.xml to convince it that it really is a 680. I would expect it to copy a new firmware image on there - then when you reboot, I would expect the Demo firmware to studiously ignore it

The Pre-boot mode might still exist though - when firmware in the form of a .RGN file can be transferred using Updater.exe - much experimentation would be required

Personally, I would expect the hardware to be intact - just because it would cost time and money to start modifying a standard device...much easier to knobble it in software.

Try the following:
Turn off the unit
Place thumb at the bottom right side of the screen.
Leave the thumb in place and turn the unit on.
Once your turn it on it should reset to factory default.