When dealing with eBay, my foremost recommendation is to check the feedback rating for the seller. That will give you the best indicator of whether they've been around awhile (ratings in the thousands), and whether they've maintained high customer satisfaction (99.5% approval rating or higher). Also check the detail of their rating feedback. If there are some negative ratings, see if they were recent or in the past. If they are recent, you may be buying from a seller who is currently having difficulties.

Once you sort out the veracity of the seller, then (imo) it's just a matter of buying what you need based on whatever criteria you have.

Having bout four laptops on ebay now, I've found the best deals by identifying specific models with the features you want and searching for those. Then ask the seller for the serial number and contact the manufacturer and make sure you have at least a year or two of warranty left on it.

You might also want to consider checking deal sites for dell deals. I know they have desktop deals, maybe they have notebook deals as well. Check out FatWallet.com

First - CraigsList - local and educated user base, sometimes you can try before you buy.

Second - Ebay
- watch shipping costs, if they are not stated, ask.
- stay away from pawn shops, and dealers that sell everything from laptops to beanie babies.
- the best seller is just a "guy" who is selling one laptop that he owned.
- IBM has it's own eBay store, and perhaps other large manufacturers do as well

1) As LotsOfLaptops said, checked for the serial number in the manufacturer site, if it is still in warranty period can fix a lot of problems
2) Battery life: some batteries have a "life" indicator. Ie, If a good battery is fully charged, pressing a button will light up 5 leds, bad battery only lights up 2 leds..etc.
You may try to ask the seller about that.
3) I got a keyboard problem when I got a laptop 9 months ago on ebay, luckily the laptop was still in warranty so I can repair that with no cost (The seller, also in Canada, didn't reply my emails)
4) I live in Toronto, Canada. Now I find a local shop who sells refurbished laptops (from corporates). I can go there and physically try them out (booting linux...etc). The price is comparable to Ebay. You may want to look at your local computer paper to find those.

This is something that I'd never buy via eBay. If you're convinced that you want used -- then corporate refurbishes are the way to go.

My personal experience, however, is that the bundled new laptop is the way to go. I've had very good luck with $800 laptops from HP over the past 3 years. But ... say you kill a keyboard, or fry out a DVD drive, or purchase software upgrade ... etc. ... you'll be then shocked to find that to rebuild an $800 laptop costs > $1600. Consider then when paying $400 for a used laptop on eBay plus having to fork out-of-pocket to get the latest virus scanning, OS upgrade, etc.

Try both the IBM and Dell refurbished sites these laptops are a great deal and come with waranties, my last two laptops were both rebushed ones (No complaints to date)