Yes, I did mean point of sale.
It looks to me that it would be possible to double spend/over spend if the goods/services are provided before the payment has cleared the blockchain. For example, I buy a laptop at the Apple Store, I submit a payment (knowing my wallet doesn't have enough in it). They see the pending transaction and I leave the store with my product. Ten minutes later they find the transaction fails on the blockchain.
Right, if you were buying an expensive product I think they might want to see that you get a confirmation before they let you leave the store. However, if you think about it, almost all restaurants let you consume the food before you pay anyway, no matter if its btc or cash you've already eaten by the time they give you the bill. Just like you can send a bad transaction and then run, you can also just plain run without sending the bad transaction. Restaurants already work on a "shame" system anyway where you just risk getting shamed if you don't pay.