I doubt its illegal. You might violate some companies terms of service though.
Trading bitcointalk.org accounts is allowed because a ban of those trades is considered unenforcable. It would be impossible for mods to enforce the rule, because sales would just happen elsewhere. It is however discouraged for the reason you stated. It allows someone to buy a trust rating.
Selling a "trusted" paypal account is certainly not a crime. Many things are used for money laundering and illegal things. I hear knifes are dangerous killing instruments, yet people use them daily to butter their bread. Dont jump to conclusions, I cant speak for paypal, but most bitcointalk account sales probably happen for paid signatures.
@bold: I meant Verified PayPal account. I am not jumping to conclusions dear but accounts which are verified and sold, can easily be used for Money Laundering purposes.
And about Knives being used to butter a bread and that being compared to buying an account? LOL
One may use a knife to commit a crime but in that case, the company or brand who manufactured the knife or sold the knife is not blamed. In the case of an account, the person who originally owns the account is blamed if the buyer is a fraud.