I usually use SquareTrade for warranties. But so far, I've called them and confirmed that only used items purchased in Ebay are covered by them. This pretty much takes them out the table for Swappa purchases. Had to dig through several layers of pages in their website to find that in writing, even after their customer support claimed it wasn't there to be begin with.
The only other company I've seen offer a warranty without needing a new purchase is GoCare for $69/1-year or $129/2-years. Their terms state: "Regardless of whether your device is new or used, as long as it is 100% functional with no prior problems, issues or damage, you may purchase coverage if available for Your device." They have a good BBB rating and...apparently, they cover rooted phones too.
Amex also covers purchases up-to 10K for 1 year after manufacturer warranty for free. Unfortunately, it doesn't cover accidental damage, which is more likely to happen on a mobile than manufacturer defects.
Any suggestions, other options I didn't consider? What are you guys using for used phones purchases?
Some background info: My wife and I are original unlimited-data Verizon customers. We've taken good care of a couple of old Droid Bionics and never had to upgrade until now, when her speaker started crapping out. Mine is still good, rooted with frozen bloat-ware, it's still doing decently. I'm not about to pay $30/month more to Verizon for the cheapest shared-data bracket we fit into. Screw them.