Besides what the item looks like there are
KEY FEATURES AN ITEM MUST HAVE TO BE AUTHENTIC.
*If the item has all four it is definitely authentic.*
The first two features are usually replicated in knockoffs, but all Juicy Dog Clothing items have them depending on the style of course.
First: (Most if not all Juicy Dog Clothing Pieces have this)

"Doggy Couture" Embroidery on left front leg of item.
Second: (Hoodies, Coats, Rain Coats, etc. have this)

Scotty Dog Embroidery on the hood.
The last two features are usually
not replicated in knockoffs, so combined with the first or two features from above you can definitely know if the item is authentic.
Third:

Juicy Couture Label. (This is stitched in different places depending if you have a shirt, hoody, coat, etc.)
Fourth:

Made in China Label. (This is stitched in different places depending if you have a shirt, hoody, coat, etc.)
So if you have 3 or 4 of the features then you most likely have an authentic product.
Just some notes from buying on eBay.
- If the seller is using stock photo they most likely have a knockoff.
- Authentic sellers will have pictures of the actual product and might even show the juicy couture label.
- If you are not sure if their item is authentic then just ask. Usually authentic sellers will respond to you and the ones with knockoffs will not answer your questions.
I hope this helps! If you have anymore questions about juicy couture items you can send me a PM anytime ^^.