The majority of designer goods on eBay are fake. I don't know that Juicy Couture purses and accessories come with serial numbers on them. Pictures are not always the best indicator, either, because many sellers use other pictures to sell their items (I've had my item pictures stolen by another eBay seller before!
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The price does sound right, but I think for a carrier, you might want to invest in something durable. What if it breaks while your baby is in it?