I am normally able to sell for enough extra on ebay to cover their fees and then some. If you follow the Paypal Rules, you are covered from scammers.
Fred Miranda sellers typically get a lot less than ebay sellers, and end up paying the Paypal fees. There is no protection from scammers, so its the riskiest way to sell.
Last I checked, and last time we discussed this, this was not true. If, as a fredmiranda seller, you use paypal non-gift, the paypal agreement provides the same level of protection from scammers that it provides to those who use their service via ebay.
It is true that the fredmiranda site itself does not provide any protection. In general, it is as risky or safe as the method that you use to collect payment given the parties with whom you transact. Much like ebay, it's possible to check the bona-fides of counterparties. Since it's a forum, you can also check if your trading partners appear to be legit (e.g. do they participate in the forum outside of trading gear ? Do they have a professional website or a flickr or smugmug page ?)
Ultimately, how "risky" the different methods are is an empirical question (e.g. what is the expected loss per transaction for a buyer/seller for each method ?) I don't believe anyone has posted much in the way of hard facts on this (here or anywhere else).