D3v1L80Y said:
You can get a good deal if you are careful and check out a person's feedback closely, both positive AND negative first.
Check to see if they deal in Mac's on a regular basis. If all the person has sold are spoon collections, and all of a sudden they are selling laptops, be weary - it could be a hijacked account.
If they DO deal in laptops regularly, contact them first. If you just found the auction and it is up in 30 seconds, best let it go. If there's a couple days left and you contact them regarding the legality of their auction, they should get back to you reasonably soon regarding their tangable goods, otherwise it could just be another auction entry that blows the proverbial smoke.
If you're looking for a new PowerBook, I would go the safer route and get it directly from Apple. It's far better than the headache you'd go thru if you were ripped off.
Now, used iBooks / TiBooks, eBay would be a great place to look.
Good luck!