"It's a bargain. It was on sale. It was half price."
Something is only worth what someone else will pay for it. Unless you are in the business of reselling stuff you bought a low price then why bother about the promotion?
If the price is important then there are always alternatives that are cheaper in almost every market. The designer top that is a bargain because it is half price, is still about 2500% more that it cost to make. Is it really a bargain?
And if you are a brand owner or retailer, why not sell out at full price?
Fix your product. Fix your service. Customers should be happy to pay more for a scant supply of something valuable to them.
Unless you are a commodity. Then the best thing you can do is realise you are a commodity and structure and price yourself accordingly. The problem with a race to the bottom though, as Seth would say, is that you might win.