depends if he selling with box or without, den with manual or without, if with manual, take it out, flip to 1st few pages, look for box contents, den match the things, otherwise see what does the guy say he is offering the set with.
next is to check the camera... that will be the hard part... not sure about canon system, best is you can get a lens and test it out, den shoot extreme dark & bright pics to see if there is any dead pixel on the LCD, etc...