16 CFR § 233.1 - Former price comparisons.
(a) One of the most commonly used forms of bargain advertising is to offer a reduction from the advertiser's own former price for an article. If the former price is the actual, bona fide price at which the article was offered to the public on a regular basis for a reasonably substantial period of time, it provides a legitimate basis for the advertising of a price comparison. Where the former price is genuine, the bargain being advertised is a true one. If, on the other hand, the former price being advertised is not bona fide but fictitious - for example, where an artificial, inflated price was established for the purpose of enabling the subsequent offer of a large reduction - the “bargain” being advertised is a false one; the purchaser is not receiving the unusual value he expects. In such a case, the “reduced” price is, in reality, probably just the seller's regular price.
(b) A former price is not necessarily fictitious merely because no sales at the advertised price were made. The advertiser should be especially careful, however, in such a case, that the price is one at which the product was openly and actively offered for sale, for a reasonably substantial period of time, in the recent, regular course of his business, honestly and in good faith - and, of course, not for the purpose of establishing a fictitious higher price on which a deceptive comparison might be based. And the advertiser should scrupulously avoid any implication that a former price is a selling, not an asking price (for example, by use of such language as, “Formerly sold at $___”), unless substantial sales at that price were actually made.
(c) The following is an example of a price comparison based on a fictitious former price. John Doe is a retailer of Brand X fountain pens, which cost him $5 each. His usual markup is 50 percent over cost; that is, his regular retail price is $7.50. In order subsequently to offer an unusual “bargain”, Doe begins offering Brand X at $10 per pen. He realizes that he will be able to sell no, or very few, pens at this inflated price. But he doesn't care, for he maintains that price for only a few days. Then he “cuts” the price to its usual level - $7.50 - and advertises: “Terrific Bargain: X Pens, Were $10, Now Only $7.50!” This is obviously a false claim. The advertised “bargain” is not genuine.
(d) Other illustrations of fictitious price comparisons could be given. An advertiser might use a price at which he never offered the article at all; he might feature a price which was not used in the regular course of business, or which was not used in the recent past but at some remote period in the past, without making disclosure of that fact; he might use a price that was not openly offered to the public, or that was not maintained for a reasonable length of time, but was immediately reduced.
(e) If the former price is set forth in the advertisement, whether accompanied or not by descriptive terminology such as “Regularly,” “Usually,” “Formerly,” etc., the advertiser should make certain that the former price is not a fictitious one. If the former price, or the amount or percentage of reduction, is not stated in the advertisement, as when the ad merely states, “Sale,” the advertiser must take care that the amount of reduction is not so insignificant as to be meaningless. It should be sufficiently large that the consumer, if he knew what it was, would believe that a genuine bargain or saving was being offered. An advertiser who claims that an item has been “Reduced to $9.99,” when the former price was $10, is misleading the consumer, who will understand the claim to mean that a much greater, and not merely nominal, reduction was being offered. [Guide I]