Riiight...
Some guy (gal?) who says he's in England is going to sell you nine $1700 computers that can't possibly be more than three months old for $650 each, and ship them to the US for free, but will only accept payment in cash or money order. Sure, that's legit.
(I might add that even economy shipping from the UK to the US should cost at least $100 for a G5, probably twice that.)
They also don't even bother to explain why, exactly, they've got $15,000 worth of nearly-new computers laying around that they're so desperate to get rid of they won't even auction them to get two or three times what they're asking--only a buy it now price of 1/3 that will do. Nope, nothing in the listing but a chunk of text and one image copied form Apple's site.
I don't think I've ever seen a more painfully obvious fradulent auction, and I'd guess it's a hacked account.
If all that weren't enough, why does the seller seem to be specifically trying to sell to the US ("free shipping within the US", price in USD), when they appear to be in England? Maybe because it's a whole lot easier to rip somebody off when they send a money order to another country. They're probably not even in England--some Eastern-bloc country, more likely.
Seriously, if you were trying to sell that much hardware, don't you think you'd maybe ask around locally, where there are probably dozens of drooling Mac users willing to buy them for twice what you're asking, or at least leave the items open for auction where the price would undoubtedly be bid up much, much higher?