There's nothing stopping you from receiving an iPhone, taking a photo of a brick, and getting a refund either. The payment provider will most likely side with y

There's nothing stopping you from receiving an iPhone, taking a photo of a brick, and getting a refund either. The payment provider will most likely side with you and refund your money, unless you do it repeatedly, in which case they'll investigate before just refunding. The difference with a third-party escrow is that they should not have a bias towards either the buyer or the seller. The traditional markets are clearly biased towards the buyers because they don't want to lose buyers from their platforms. They don't want to lose sellers either, but the risk is smaller, because it's more difficult for a seller to switch to using another platform, and a certain amount of fraud is kind of expected from sellers. The use of one or more independent escrows can prevent the marketplace from unilaterally taking money from the seller and refunding the buyer without performing their due diligence (which PayPal frequently do not)