If I'd noticed--I didn't happen to find any to purchase in that price range(and I'd used my book allowance already
)I would have been annoyed. I don't know about a 'huge black mark', though--it was, after all, a sale; giving us something extra they didn't need to. Maybe only a small black mark, or a large dark-grey one. Of course, since the point of a sale is to inspire kind feelings and generate business, the glitch caused it to fail miserably and should be very embarrassing to all concerned.
They seem to be having some problems in general. I've found several mistakes in their descriptions and thumbnails lately, and frequently the 'blurbs' have problems with hyphens and other format problems. Once they attributed a book to the wrong author of a similar name! They corrected it but I wonder if they had to reduce staff or something.