Very reliable. They’re a well known company and do well because people know they have good service. They deliver very quickly and have a great policy regarding returns on items.
endless.com is also good, prices are better then Zappos, and you also, have a year to return, unworn shoes. Free shipping and returns as well.
6pm.com is a division of zappos, but i think there is a fee to return. Their prices are even cheaper, than zappos so if there is a shoe, you like and know the correct size you need, it might work for you. good luck.