From my understanding, if it's an Expired Domain, you can pay anyway you wish.. Credit Card, Paypal etc. I do not think escrow is an option, but I could be wrong on that.
If it's a user submitted domain, anything over $500, Escrow.com is used.
I've sold a few there. For anything over a certain $ amount (I think $500), they send both parties to escrow.com. It's been a year or since I've done one there though, no telling if they've changed it.