I have to say I did not get them from Amazon but I assume they would not sell fake Uggs.
Authentic Ugg Ultimate Short are very well made and super warm. I also like that they are not as ...well ugly :) as classic UGGs.
I think thicker molded outsole reinforced toe and heel make them more of a outdoor shoe. My pair is over five years old and still looks great. I got light beige color(sand) and would not wear dark wash jeans over them as color might rub off, especially when it's wet outside.
I find UGG sheepskin care kit helps keep them clean and waterproof.
I usually wear 9.5,got this pair in 8 and it fits perfect.