(they'd be pretty useless if they did, anyway- where would my refund money come from?)

Almost sounds like you're confusing escrow with insurance?

Your refund would come from the middle guy entrusted to securing your funds until your goods were delivered as promised. If your goods are not delivered, or if what you ordered was nothing like what was promised, the escrow service would simply send your bitcoins back to you, instead of sending them to the merchant who tried to defraud you.

These services would likely charge a transaction fee for the service.

Even silk road offers an escrow service that is apparently effective enough. The scammers on silk road typically try to con you into closing the transaction before delivery of any goods, so one red flag that you may be looking at a scammer is a number of early settled transactions in their history.

If someone wanted to do something like this more mainstream, they could develop a third party bitcoin escrow service that offered an order history, rating or feedback system, and transaction comments from both parties. You could even develop a rating score formula similar to a credit score, where older accounts with more history, have higher scores, which make it much harder for scammers to use throw away accounts.