ive had several online transactions and i only did it thru bank to bank transfer. also have a video conference with the seller. facebook alone is not enough since its only pictures that you are seeing. if the item sold is too good to be true then better let it go. if he/she is a compulsive seller then better let it go. if he/she doesnt agree to bank to bank transaction then let it go. DO NOT settle for western union/gcash/mlhuillier mode of payments especially if your purchasing expensive items. remember the buyer is always at risk when purchasing online as the buyer will conduct the transaction first.