In reply to Spike:
I personally avoid refurbished laptops or business sellers.
A refurbished laptop it means a laptop that was broken and got fixed 'somehow'. That fix is unlikely to have been back to manufacturers specs, but the cheapest the 'refurbisher' can get away wth to maximise profit. "Manufacturer refurbished" which is a misleading term most of the time, is a warraty return that was not economical to repair, so you got to think how come that laptop is now being sold.
Also there's no way to know what's inside. That is, you check the specs online, decide it fits your requirements, but when it arrives it's nowhere close to what was meant to be. So if for example a particular model had X amount of Y speed Z brand RAM, once it comes from a refurbished jobby chances are it will have the cheapest sticks that fit, and won't perform anything like the original laptop was meant to. The same will apply to every other component in it.
Likewise, business sellers are in for the profit, so if a particular model of laptop is worth, lets say, £500 in the used market, the seller will have bought it much cheaper than that, lets say £350 in order to sell it for £500 and make a profit after seller fees, postage, tax, etc.. How did he come across a £500 laptop for £350 is what i'd be asking myself.
On the other hand, a private seller is simply selling at the market rate an item he bought and no longer needs. Any existing problems if not disclosed will be apparent soon enough, and more often than not at least is not a laptop that was already faulty and someone tried bodging a fix to sell it on which is what you get with refurbished laptops and business sellers.