>So if a potential buyer sees something 70% discounted, that implies that originally, the market determined that higher price as a fair price: a price that at least some buyers would pay for this item. The buyer trusts the market that that is apparently a fair price, but today the buyer is in luck, because it's been discounted to below the usual market price!
This whole paragraph is wrong in my opinion. A 70% discount does NOT imply anything other than it's 70% off of some number that the seller is free to decide, since they own the product they are selling and I'm not aware of any laws dictating what they have to sell at.
The second part I don't agree with is a seller selling at "below" market price. There is no such thing, unless the seller is doing charity work. When a sale happens, that is at the market price, unless of course there is some collusion where the buyer and seller agree to do some other trade-off to avoid paying taxes, but that's neither here nor there in this conversation.
On popular sale days, such as Black Friday, the sellers aren't selling below market price. They are selling at the price that they think they need to in order to get the publicity/feet in the door that they think will lead to other sales. In effect, the seller is buying the buyer's time and attention and whatever probability the buyer has of spending more money on other things with the "discount" they offered.