I think this applies to more than just (Mac) apps. Coupon codes, flash sales, and other deep discounts have a tendency to trigger buyers remorse at checkout.

I was fine paying $ X until I found out that I could have paid 50% less last week. Now, if I buy your product, I feel like the only idiot that paid full price - a price I was happy to pay 5 minutes ago.

If you aren't able to sell at your current price point, you should evaluate why and either fix the issue or lower your price (permanently) to match what users are willing to pay for it.