engine - 8:32 am on Apr 19, 2012 (gmt 0)
Mrs engine just had exactly this situation. She ordered a new dress for a wedding we're attending, so it wasn't an ordinary outfit.
The item arrived the following day.
In addition, in her email that day was a discounted price for that very outfit.
She called the company and they said they cannot retrospectively discount the item, but suggested the item is returned for a refund, and re-ordered at the new discounted price.
That's what she did.
Both seem happy with the arrangement.