Other than that just the basic stuff. Members with a longer history or that are "gold members" are usually a safer bet. Don't haggle prices on the open forum, send a direct message for that. Don't post phone numbers or email addresses on the open forum, again, send a direct message for that.
I personally will not pay anyone using "friends and family" settings on any payment service unless I actually know them or have done business with them before. I will pay the fees on PayPal to process the transfer as a "sale transaction" unless the seller included the fees in their pricing. Some do, some don't. Get a tracking number, make sure the insurance on that method of shipping will cover the value of the item or buy extra insurance.
