I have never had a problem with this site. In fact, literally everything I have ever bought has fit nigh perfectly, with the exception of a single bra (flimsy) and a pair of leggings (too small). I am plus sized, very tall, with long arms and a curvy shape. It is almost impossible for me to find clothes that fit well, including in more expensive brands (Michael Kors, Tulle, etc). It is so rare to walk out of a physical store with anything that I truly loved and that really fit nicely. Every time I open a package from Zulilly, it is like everything in it was made for me. The pair of jeans I am wearing right now is just out and out perfect. That NEVER happens. As a fat person with very big hips and a small, high waist, getting pants that work and aren't horribly uncomfortable is like finding a unicorn. But Zulilly just keeps giving me unicorns! I am happy with everything I get.
I want to defend them a little bit too: do not buy from any website before you have read and understood the return policy. I read it all before I bought anything and thus the lack of returns and the time it takes to ship were not surprises to me. I don't buy things I need fast from Zulilly because that is simply not what they do. But through them I can get 500$ worth of clothes for 200$. I call that a win. Another strategy is to buy things a size up from what you need so that if it turns out too big you can easily have it tailored down for not very much money.