With listing of anything on the bay, describe as though you have no pictures and picture as though you have no description. Try not to use any negative words or sentences in your ad.
Put in all dimensions and yes, you can state that it is authentic as long as you know it is. Saying it is authentic is not the bad thing, it is making a big deal of it, which the people who are selling fakes do.
Get a good camera, it doesn't have to be the most expensive and the one with all the bells and whistles, it needs to take good clear pictures.
This is the best way to describe how to sell on ebay, I love it!