First, did you just format them using the option on the computer? If so, I would format using the instructions that lattesurf provided here:
How To: Removing Memory Hack. Only then can you be certain. I formatted mine using the computer tools and it still showed the hacked memory.
Second, AMV files are definitely losing popularity, but there is always a market for anything that looks like an iPod.
The 8GB size puts me off though. It just screams memory hack to me.