Not once have I gone to Fifi's and not found something wonderful for myself or someone else, at a great price. I am a 0 - 2 with very skinny legs, square hips and a flat butt and have found several pairs of designer pants that fit beautifully, and wish there were more.
The sizes I've found range from 0-18 with most in the 6-14 range (some XL and XXL). As with anyplace, the stock comes and goes and you have to come in frequently and buy on the spot if you want it. There usually is a nice selection of designer clothing and they are picky about the quality of the clothes they consign.
I would recommend that people who shop in consignment stores also help by bringing in their gently used clothing to keep the stock fresh and varied in sizes and styles. If you don't bring in the sizes you want to buy, you might find no one else is either.