Paypal has been around for far too long not to have security settings in place...
however, here's what I can tell you from personal experience.
1. She needs to log into her Paypal account and verify the money is there.
2. She can talk to a customer service agent at Paypal 24 hours a day to verify her funds.
3. He cannot take his money back - but Paypal can take it back if he reports the item not as described. however, they have to prove the item was wrong and show proof of return postage service.
However, when I sold a ring on Craigslist - the guy who offered to put $100 extra for overnight shipping - it was a scam...sent a really good Paypal looking notice that I had received money but when I logged into my account - the balance did not reflect that payment.
Do NOT send anything until the money has been confirmed by Paypal..She can can even have the money transferred TO her checking account.
I would avoid things like this - especially when someone offers to pay more or for shipping than it really costs...please feel free to inbox me for more information.
bottom line - you can get scammed ANYWHERE - many people have lost their moral compass...
Paypal will NEVER send you an e-mail stating that the funds won't be credited until a shipping is confirmed...NEVER EVER!!! They get the money, they tell you they got the money, you check your account and verify the funds are there - THEN you ship.