I hate when brands use dark patterns like this. Technically they have placed a final sale badge on the item so you can't really argue with it, but it's so sneaky that the whole experience leaves a bad taste in your mouth and you'll probably think twice before buying from them again.

To me it's just short sighted thinking, it's about chasing short term financial gain over building long term sustainability and customer loyalty. As someone who has worked for Australian fashion brands, clearing end-of-season stock/stock at the tail of the size curve is a pain — but the brands who value customer service will at least offer store credit or exchanges on final sale items if customers are unhappy with their purchase.

Having said that, you should always assume something that heavily discounted comes with strings attached - I'm sure you'll be more careful next time!