This is not completely accurate, the FTC has rules against deceptive pricing practices [1]. I'm not sure how often these rules are enforced and what the penalties are though. They specifically give an example where raising a price before a sale is not allowed:

> 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.

[1]: https://www.ecfr.gov/cgi-bin/text-idx?SID=f8c45f090a32596673...