I don't always have success with Rethreads (either buying or selling), but it's my opinion that the State street location is on the up and up. The guy working was super friendly, and he looked at my items I was selling in under 10 minutes. They ended up taking 3 items - a pair of pants, flats, and sunglasses - for $39 in store credit.
Sometimes it's hit or miss, but any resale store is! It's always well-organized and clean when I visit. Since the store credit can be used at either location, it's worth trying to sell and save up the $$ and wait til you find something good!