like this, although I appreciate that's no comfort to your friends' son. To be fair to PayPal they do display very prominent warnings on their site and it's difficult to miss these when siging up for an account. They display icons alongside those items which are covered by their buyer's protection scheme, and they'll pay out up to £250 by way of refund in cases where goods are paid for but not received.
PayPal aren't the sellers - they're simply a payment handling organisation - and it's not really their fault if someone doesn't make the recommended checks before parting with their money. PayPal process millions of online payments a week, and they have an excellent reputation in the e-commerce world. It's unfair therefore, to advise caution when using them - better to advise caution when purchasing something from a complete stranger and sending them the money without making any checks whatsoever. After all, why should PayPal or anyone else protect people from themselves?