1)Check for cosmetic defects on the body and/or lens
2)Check the box for all the supplied accessories
3)MUST have warranty card
4)Ask for a lens and memory card to 'test' the camera.(however, if you go back and find the camera not working, I believe most shops would offer a 1-to-1 exchange within 1-2 days.)
5)Last but not least; check for shutter count once you're home.(If you're that worried)
Regarding the 5th point; recently there was a ClubSnap member who bought a new camera that had a 400+ shutter count. This would obviously seem like the camera was used as a test camera.