I have been thrilled with the items that I have ordered for my children: clothing, toys, books, food and more. Good quality, good fit.
The things that I have ordered for myself (5 different shirts) have been undersized by about 3 sizes (I ordered UP a size just to be safe, too!).
I ordered some bar stools from Linon Home through Zulily recently. One was missing parts, the other was made with rotten wood. It took 2 months for a resolution. Zulily's customer service was AWESOME throughout the process.
Remember that Zulily is not making or selling these products, but are allowing others to do so through their site. I don't blame Zulily for the poor customer service that I received from Linon Home, but I do blame Zulily for continuing to allow the clothing sellers to mismark their sizes and sell on their site.