Strike Through ("was/now") Pricing
Amazon strike through pricing on Shopify will be in effect automatically if the "Compare at price" in Shopify is higher than the price the product is for sale at on Amazon. This is similar on Magento and Woocommerce where 'price' should be lower than 'list price'.
eBay Strike Through Pricing is only available to qualified sellers who participate in the Discount Pricing program. Please Contact eBay to apply.
Once enabled on your account by eBay, if your 'price' is lower than 'list price/compare at price' (both set in your ecommerce platform), strike through pricing will automatically occur.