Money sent through PayPal and any other money transfer service that accepts credit cards can be easily reversed by the sender, even after several weeks. Therefore, you should only accept PayPal in trades with people you trust very highly.
This is why newbies are not likely to sell their PayPal USD for bitcoins successfully.
Some other services that are not totally safe:
- Bank transfers (ACH, etc.) except wire transfers
- Most gift cards.
- Moneypak
- AlertPay
- Paysafecards
- Dwolla
- Western Union (they reportedly will sue the recipient to recover money in some cases)
Perhaps someone could be kind enough to explicitly mention what forms of payment ARE safe and likely to be accepted by traders here?
You are on Bitcoin forum and you ask about safe form of payment?

One of the main advantages of Bitcoin and many other cryptocurrency payments is that are non-reversable. Usually, several network confirmations are required to be sure. However, you are sure that such threats that you may encounter on the services listed by themos will never meet you with Bitcoin.