Alot of people on this forum are falling victim to PayPal chargebacks, while this is avoidable. I'll explain.
There are 3 ways a buyer can file a dispute:

    * Goods were not delivered. [/*:m:2teempap]
    * Goods were not as described. [/*:m:2teempap]
    * The transaction was unauthorized [/*:m:2teempap]


Goods were not delivered and not as described

The problem is, if you just accepted the buyer's payment, without taking precautions, you will lose the dispute.Now, what can you do to avoid this? First of all, you have to request the payment, do not let him send it to you. In the comment section of the request, you put the following text:

By payment, you signify understanding and acceptance with the following. This is payment for virtual goods and is nonrefundable and not protected by paypal's buyer protection policies. By payment, you acknowledge receipt of goods and satisfaction. You waive right to dispute payment on grounds of receipt, quality, description or any other reason.

When he does file a dispute, just tell paypal to look at the comment of your money request and you will win the dispute. The buyer confirmed he received his goods, intact, as ordered, so he can't do a chargeback.

KEEP READING, YOU ARE NOT YET FULLY PROTECTED.

Unauthorized Access

You will need to ask the buyer's personal info to be protected against this. Some people will make a big deal of asking for their personal info. Do not deal with paypal accounts if you don't know if they are stolen or not. Its better to make $50 in 2 weeks, then $300 a day if the $300 is going to get chargebacked.

If you accept a payment from a stolen PayPal account, YOU WILL GET CHARGEBACKED. So how do you know if the PayPal account is stolen? If there address is confirmed with PayPal, and you call their home, odds are the account is not stolen. Keep reading.

Ask the buyer to send you an invoice, he can do that by going to "Request money --> Create an Invoice". Ask him to include his address and phone number. If he doesn't want to do that, abort the trade, it's not worth it. If you do continue, expect a dispute in a few days.

If the buyer doesn't know how to make an invoice, refer him to this guide, more specifically to the screenshots below:

Address and phone number:
http://img510.imageshack.us/img510/6697/invoice1wp8.jpg

Invoice itself, note that 1 Yen is less than 0,01€:
http://img510.imageshack.us/img510/2800/invoice2jn4.jpg

You don't even have to accept the payment as a buyer, you will find the address and phone number in the email sent by Paypal, or by clicking on "Details" of the payment:

This is what the email should look like:
http://img180.imageshack.us/img180/6213/invoice3tm8.jpg

If the address and phone number aren't included, ask the buyer to send it again, including both. If he can't, call off the trade. Now, look up the buyer's name in an online phone book, 411.com for the US or http://www.bt.com/phonenetuk/ for the UK. Make sure address and phone number match.

Then call the buyer, and verify if he knows about the trade, if not, inform him that someone has access to his Paypal and that he has to call Paypal to block out his account.
If he does know about it, you know you're not dealing with a hacker, but the person could still scam you, so keep reading.

Now, before you request the payment, let the buyer send you an email WITH HIS PAYPAL EMAIL, NOT HIS MSN EMAIL OR ANOTHER RANDOM EMAIL with the content. "I, <buyer's name>, confirm I'm buying <goods> for €<price>". Now, make sure the buyer accepts the requested payment within 5-10 minutes. So if he ever claims it was a case of "unauthorized access", you can provide Paypal with the buyer's IP and the timestamps of the email (you can extract this from the email header). That way, they can check if the IP's from the buyer's account and the email match, if they do, they know the buyer is lieing and you will win the dispute.

(Refer to this guide if you want to know how to do extract the sender's IP from an email header: http://www.johnru.com/active-whois/trace-email.html)