But is it cheap to do that?
And if I have to go to the postal office every time that I do a transaction would be very annoying.
I prefer to focus on bitcoinmarket security measures.
You can only use PayPal, if you have some bitcoins in your account, the more bitcoins you have, the more you can buy using PayPal, thus if you do funny stuff with PayPal, you risk losing all your BTC.
Thats nice. But first How do you buy the bitcoins ?. And, where is the benefit there?. If I want to sell all my bitcoins and my only method is PAYPAL I can't... because I must always have some bitcoins in the account. Trading will be more difficult, although I think is not a bad idea to be considered.
I think is easier to hold the buyers BTC until is not possible to open a dispute in paypal for that transaction. But it would be annoying to for new buyers. And I think that punishing all the users for just a certain % of scammers is not the way.
Another Idea: We can use the same confirmation method as bitmarket plus a real ID confirmation, like a document, a credit card bill and so on.
Therefor it would be a lot more difficult for scammers to operate.
Obviously, people who uses PAYPAL takes the risk, but for many of them is the ONLY WAY (as me) to cash out the money, or to deposit for buying BTC.