Examine it closely and you can most likely fix it easily yourself. If it is more than simple repair, then you might need to contact Keystone for warranty work. You may want to let them know about it anyway.
Of course it should have been taken care of, but since it wasn't, your reaction and response will impact whether you enjoy your trailer or not... take it as things happen and move forward, don't let it (or the number of things you will find as you start using the trailer) dampen your enjoyment.
We had to fix our couch when we bought our trailer (used but excellent condition). I ended up putting a vertical brace under a split horizontal piece to support it. Never had a problem with it after that.