The big tip off is definately the sketchy details combined with the fact that there is no pic and the seller has a zero feedback rating... While everyone has to start there at Ebay, this sort of thing smacks of scam.
I would be curious to see what the person who ends up buying gets...
Anyhow... I guess that with enough patience and skill, one could fabricate their own PPC accelerator for the a500, but even as a decent electronics person, I don't think I would have enough time/money/patience to undertake such an endeavor and I feel you'd have to "doctor" the ROMS too would you not?
Anyhoo, I wouldn't invest in this one ;-)
