If you get a used one from a human-being, you can ask them to check the firmware version for you.
Exactly! ... as this is what i did BEFORE i bought mine on ebay to make dang sure it was a v1 player and all was good once i got mine.
basically to sum it up...
"Rockbox doesn’t function on the newer v2 models. They can be identified by checking the Sandisk firmware version number under Settings → Info. The v1 firmware is named 01.xx.xx, while the v2 firmware begins with 03."