Google shows a strikethrough sale price only when the discount is over 5% and under 90%, both prices appear on the landing page, and the base price was charged for 30 days within the past 200 in markets such as the UK, France, Germany, Spain, India and Brazil. For US Shopping ads it is 5 of the past 30 days or 15 of the past 200.
Merchant Center's misrepresentation policy requires the full cost, including shipping and fees, to be clear before purchase. In the EU, an announced price reduction must quote the lowest price of the previous 30 days as the prior price. India's CCPA guidelines ban dark patterns such as false urgency and drip pricing.
On Meta, dietary, weight-loss and health products must target people 18 and over and can't claim to cure conditions; general food and non-permanent cosmetics are exempt from the age rule.