The buyer does NOT need anything more than your paypal ID to send you money. You can also give them your name and address since they need to know you are honest, but I would be careful what you tell them unless you are SURE about who THEY are. NEVER pay for an appraisal or other service the buyer asks for. If the domain is somewhat expensive, consider using an escrow service like Escrow.com. There is a fee, but it will protect both the buyer and the seller.
In most cases the seller gets the money, then they push the domain into the buyer's account, OR they help the buyer with the transfer of the domain to the buyer's registrar.
1) Get as much information about your buyer as possible. Do searches in Google for their name, address, phone number, and email address to see what you find. If you know a domain they own, Check the WHOIS information to see what it says. Get their name and address and business address if possible.
2) Never give them bank account, social security, or other personal information. Give them your name and contact information, since you want them to trust you also.
3) Never give them the domain unless you really feel you can "trust" them, AND you can afford to lose the domain if they are a crook. If they want "proof" that you own the domain, you can change the name servers to theirs before you give them the domain. If they don't pay you can easily change the name servers back.
4) After you get the payment, make 100% certain you have the money and all payments have cleared. If a credit card is used, tell them you need to wait 3-5 days to make sure there is no "Charge backs". Call your payment provider and ask them to confirm you can keep the money. If they don't like this delay, tell them you can change the name servers to theirs so they can use the domain while you both want for payments to be verified. If they complain, tell them they have no reason to object if they are honest.
5) Once you have the payment verified, do not delay in the transfer and helping them get their domain. Apologize for the delay, but tell them it is needed these days.