How to distinguish Nexus 7 (2012) and Nexus 7 (2013)
There are several physical differences


Most notable is the different orientations of the "Nexus" logo. 
The 2013 model drops the dimpled texture on the back.
The 2013 model also has a camera on the back, which the 2012 model lacks.
The 2013 model has a notification LED on the front, which the 2012 model lacks.
The 2013 model has a speaker grille on the top for stereo sound in landscape, while the 2012 model only has the bottom speaker grille.


2013:



2012: