Paypal does hold funds for 21 days on high risk items such as electronics. They also hold funds if the seller is new to eBay. Your suggestions are unrealistic. eBay really has no way of policing their sellers. If they hold everyone's money in escrow, they will go out of business fast. No seller is going to want to ship an item at their own expense before they've been paid.

If a buyer is unhappy with a purchase, all they have to do is contact the seller and if that doesn't resolve the issue, file a claim with ebay. ebay almost always sides with the buyer. If the item is misrepresented, ebay will sometimes pay for return shipping.