It depends.
(long explanation, it'll make sense if you read the whole thing)
For business laptops, I'd say yes. The thing is, businesses get substantial volume discounts if they buy a lot of laptops. So if a company goes to Dell and buys 20 laptops instead of 10, then they can get them cheaper for each. They can take advantage of this easily by buying more laptops then required to get them cheaper for each, and then sell the extra ones on Ebay, and overall, pay less on the order.
Example:
A company needs 20 laptops. The laptop model they want to buy is $1000 each. If they buy 20, the laptop will cost $800 each due to the volume discount. If they buy 30, they can get them for $700 each. So basically, the what the company does is they buy 30 for $700 each, and then sell the 10 unneeded ones brand new on Ebay for $600 each. In the end, they pay only $15000 if all the laptops listed on Ebay get sold( very likely since they're brand new and $400 under MSRP). If they bought only 20, they won't get as large of a discount, and they'll pay $16000 on the end.
As a consumer, you can buy one of the laptops they sell for $600 and still get a brand new, functioning laptop for significantly less than new.
The main factor though is that it generally only applies to business laptops. Consumer-end laptops generally don't get volume discounts since consumers don't tend to buy in bulk, so the whole thing above doesn't happen. Still, there's no reason that you can't use a business laptop for consumer purposes. They work fine as a consumer laptop. I'm doing so right now. In fact, it might even be better, since business laptops generally won't sacrifice functionality for looks as often is the case with consumer laptops, and you'll usually get a sturdy laptop with great ergonomics.