PayPal is fine if you use the system to your advantage. If you're the one paying, its not bad. If your the one receiving, it could suck hard. A lot of people exploit that, but if you cover your ass with PayPal, read their rules and play by them, then a lot of the horror stories of PayPal can be avoided. I've read them. I've also done 30 deals of $1000+ through PayPal, had 2 complaints, and never had a problem. When you ship things, certified, tracked, delivery signature, the works. If he has your money, and you don't have an object, then you can go after him.
I use ebay feedback and only deal with Confirmed members. Confirmed members have feedback, verification of identity, and a credit card / bank account or both attached. Use that, if theres a problem, you know its not a case of identity fraud (and granted, theres always that SLIGHT possibility, but if you know enough how to exploit it, you know enough that you can still be tracked down... The ones who know enough to do something aren't the ones trying to rip people off.)
3rd Party Services: I dealt a lot with paintball equipment. Buying and selling used equipment to make money. Paintball shops often will do this, act as a 3rd party... They receive both your new laptop and his money, verify the EXACT condition he described, and if its lacking, usually they'll send the respective parties their merchandice / money back, or contact you and find out how you want to proceed. I almost always used a 3rd party service or paypal.
When it comes right down to it, if you try to buy the laptop and send the money and he rips you off, then thats fraud, especially if you mail him the money and he doesn't send you the merchandice. He's now used the mail system to defraud someone and thats potential jail time. When I would buy or sell equipment, thats one thing I always said in my arbitrary conversation, was that I was fully aware of the consequences and options if the other party chose to not hold up their end of the bargain. Granted, the 2 times I had issues were with the other party not sending me the merchandice and paypal dealt with it (used PayPal both times, and it worked out fine, even if you have to wait 2 weeks for your money returned, and you lose out a little because you're not returned the paypal fee they had to pay).
Just investigate the person you're dealing with, ask for a phone number, and talk with them on the phone, go over the deal and ask exact information. Whats the exact condition of the laptop? Are you aware of ANYTHING wrong or odd with it?
Those are the rules I've followed when doign business with people online, and I've never had a problem that was not dealt with.