Is Paypal safe to use?

Few days ago, I was searching for info on Android phone online and found a lady who said she is selling a smartphones cheap
so I sent several emails and now I am about to close the deal with her
I am guessing I have to pay her through paypal and she will send me the phone when she receives her payment..right??
so I was wondering how safe is to use paypal in this situation
If this turns out to be a scam..is there a way for me to get my money back(cancel the transaction or something)??
I know many people use paypal to buy stuffs from ebay and want to know if you guys had problem with paypal??