A glitch has surfaced in the new PlayStation Store that lets trial PS Plus members download game trails, but actually reads them as full game purchases.
So essentially, you get to download games without paying the price. But when you actually get down to playing those games, your system tells you have one hour to try the game, as it would for a normal trial version download via PS Plus. But once that hour is up, it doesn’t let you purchase that game via the store, because the store thinks you’ve already purchased the game.
When you search for the game in the Store, it shows the price and everything, but doesn’t let you buy the game, saying the title isn’t available for purchase.
No real workaround for this glitch has yet been discovered, but this seems to be pretty widespread.
Keep checking back for more info.
[Source]