And then there's the personal sale angle. I'm not going to take paypal or have the ability to process credit cards for a yard sale or some crap that I'm selling through the classifieds or craigslist. Given how I'm mainly just trying to recoup something in the process of a sale, adding more hoops or steps will just result in my not bothering to sell junk anymore.
In this country direct bank transactions are used for a lot of this. It's not quite as easy as taking cash when you hand over the item but it's not much harder: give them your bank account number when they agree to the sale and then check that the money is there before handing over the item. If you're going to bank the money anyway it's actually easier. Obviously it's not practical for yard sales but it works pretty well for classifieds and online sales.