well, obviously dishonest sellers would lie. but i got an email from a seller assuring me 100% authenticity, she was even going to get the bag checked at her local givenchy story. if seller offers you a total refund...wouldn't that be a good offer??
personally, i would go with the black leather. i know patent is the thing right now, but i think i would get sick of it very soon. also, the lines of the bag are very classy and i don't think patent leather fits the style!
but in the end, if you really love the patent and that's what you want...go for it!