Visiting My Sister's Closet can be a hit or miss event. On a particular day you may not find anything you like. However, if you bring your patience and a sense of adventure you could find something fantastic!
While I have never had the opportunity to work my way through each rack and display case (but would like to someday!), I have found my favorite brand of jeans (7 for All Mankind) a couple of times at what I think is a great price. I have brought in items to consign as well. Once you establish an account, the process is fairly quick and easy. I don't dwell on which items sell, or the price, since I would have otherwise donated the clothing. Any store credit received is a fun bonus to me!
One piece of advice - try on everything - even if the label says it is your size, and it is a brand you are familiar with. Jeans, especially the designer brands, have many times been altered by the previous owner for waist size or length (and all sales are final).
Happy hunting!!