If you have a Vita and live within 10 miles of an independent used game store or worse, a Gamestop, then you've likely run into the problem of not being able to collect Trophies on used games. Let's fix this; it'll take like 30 seconds.
-Locate the game that you would like to fix the Trophies for. We're going for Mortal Kombat here.
-Hold your finger down over the icon until a little (...) badge appears on the right side of it. Click that little (...) badge and you'll get this screen.
-If you click "Information" then you will see that you are ineligible to get Trophies.
-Let's back out of the "Information" screen and go with "Delete" now. Click OK. No, it won't delete the contents of the game card, that would be crazy. It just deletes any information retained from the previous owner.
-Takes just a second
-Now exit back to the main LiveArea and take the game card out of the Vita and then just put it right back in. It will install as soon as it clicks back down, like any other new game. Now hold down on the icon again and check the information tab. You should be good to go.