Well it becomes very difficult. Allowing sellers to cancel purchases from buyers without a strong and long history of positive feedback is a start - I believe e

Well it becomes very difficult. Allowing sellers to cancel purchases from buyers without a strong and long history of positive feedback is a start - I believe eBay technically allows this. But naturally sellers are then cutting down their potential buyer pool - it's a dilemma they need to deal with. Of course one easy way to do this is cut out the entire online buyer pool altogether and sell your camera at a pawn shop - near-zero chance of fraud there. Why don't sellers just do this? Because they want more money than the pawn shop is willing to offer, so they take the risk of selling online. It's always important to remember what we are actually buying and selling a lot of the time is risk - the value of the item is often just a fraction of the overall purchase amount.