Don't buy a laptop from eBay since there is no way to confirm the condition of the screen. A laptop with a poor screen is virtually worthless.
Buying desktop computers on eBay usually means very expensive shipping cost. People often forget about that until it's too late. It might be worth considering if it's for sale locally and you can pick it up.
When it comes to large and expensive items like computers I'd stay away from eBay since it's too easy to get ripped off if you don't know what you're doing. You're better off looking in local ads in newspapers, user groups, etc. where you can examine the goods in person before you fork out the moolah.
Real Macsters don't repair permissions.
Opinions are like toothbrushes. Everybody has one, so there's no need to share. - Red Green
Sometimes it can mean an auction house has bought up a liquidated company's remaining merchandise and the display items go back into the sales mix as "open" box items. Either that, or the goods were just opened for testing.
Check the seller's feedback. See if among other sold items, there is feedback for other "open box" computers. If the feedback left for these items is positive and says something like "as described," repeatedly, then this may very well be an only slightly used computer; you might even be pleasantly surprised. If there is no similar item for feedback, or if the feedback is less than appropriate, move on.
If you do buy the item, pay by PayPal and use your credit card, not your bank account. Banks can do chargebacks for goods not as promised too, but it's easier with a credit card.
I found Manny's dual G5 on Ebay, but only considered buying it when we found out that it was in St.Jerome Quebec (driving distance). We also asked for the serial number of the computer and plugged it into the Apple site to check it (because it was coming with warranty). I then contacted the seller and arranged local payment and pickup so we went for a family drive.
We got a great deal on it. Buyer beware on ebay though, check feedback, look at the types of items the person has sold before (any other electronics, high ticket etc). Local sales of course would be preferable. Don't get caught up in bidding fever and end up paying more than the item is worth.
Ive been ripped off on e-bay numerous times for high dollar items and ive got a couple KILLER deals on e-bay for high dollar items.
First, I would NEVER buy a computer from California. Everytime ive been ripped off it was from California. Also, dont trust feedback. The last time I got ripped off it was for a $2500 Sony TR3AP notebook. The guy had 2500 feedback at %99.1 posative. Sent the money via money order (BIG MISTAKE I know, so dont think I need to be schooled here folks... ive learned the hard way) and didnt ever see any computer. So,there is a bad story...
Now for a good story.
I bought a 17 inch Powerbook on e-bay for $1800. This was about 8 months ago when they were still worth something. It was brand new, but open box. This meant the person was given it as a gift, opened it, but didnt ever use it. I immediatly turned around and sold it for $2300 here on ehmac and gave someone else a great deal, plus I made a buck and everyone was happy.
I bought that Powerbook from a guy in toronto and met in person, paid cash and picked it up from him. I wouldent have done it if I couldent have met him.
My advice after both making and loosing lots of money on e-bay, dont buy high dollar items unless you are allowed to pick it up in person. Even if you dont plan on picking it up, make sure the seller will let you. Make up a story about an aunt who lives in his town that your going to visit or something. If they say yes, your probably safe. If they say no, its a scam. Also, ONLY pay via pay pal and ONLY have it shipped to your verified address.
These tips should help protect you. However, e-bay is always a gamble. I got ripped off by accepting a certified cheque... turns out it was forged. Lost all $1600 US for my digital camera. So, dont think just because you do the right thing your going to be safe. Take every precaution. Be a jerk if you have to and dont buy if your not FULLY comfortable.