Only the valid email that connected to PayPal. The buyer only need to pay with those indormation .With the info you can pay through your paypal balance or credit cards.
If it's regarding an order , just make sure the seller is the good seller .Even if PayPal is working on both Buyer and seller protection where you can claim back any transaction that invalid ( wrong item, not recieve , etc ), but to make sure everything will be fine , you must check the seller contact address and etc . Once you're sure he/she is in a good standing, then you can make your order.
Make sure every order is NOT personal payment if you purchase things since this will not give you an option to claim a dispute if you got any problem in the future.
