Their prices are ridiculous for a second hand store with pieces that are faded, worn, and out of style. You may as well just shop in the sale section of the actual store, price will be comparable and the quality will be much better.
That being said I don't know why they are so picky about what they accept from you as most of the clothing in the store is not high end. It seems like they expect people to just donate the clothes they don't want to pay you for and that's how they make a profit in the end. It would be fine if they said that instead of saying they don't want it but can donate it, which means selling it in store and making a profit from it.