SanDisk themselves started the whole v2 thing by putting 'v2' on the back, and using the term themselves.
The problem with that is that SanDisk is also known for just taking whatever parts they have on hand for refurbishing older Sansas. Therefore, you may buy a refurbished v1
Sansa, but it'll have the back cover of a v2 Sansa, and the only way to find out for sure what you got is to look at the firmware version.
I should know; I purchased two c240s from Woot once, and both had v2 backs but were v1 internally.