Your personal data may not be completely removed with an Android factory reset

You just received your shiny new flagship of a smartphone and now you are ready to put the old one up for sale on eBay, or Craigslist, or Swappa. The secondary market is alive and well with over hundreds of thousands of devices for sale.

You have taken really good care of your older Android device and are certain that it will get a great price from an eager buyer. All you need to do is perform a factory reset and you are good to go, right? Maybe not.