expression, noun
amazing bargain; fire sale; selling at a loss
Figurative expression literally meaning 'bleeding great service'; used for a sale or deal where the seller is offering an exceptionally low price, as if taking a loss. Often used in advertising or casual speech.
閉店セールで出血大サービス中です。
We're having an amazing bargain sale for our closing.
あの店はいつも出血大サービスをしている。
That shop is always offering incredible deals.
捨て売り means 'selling at a throwaway price', often for clearance; 出血大サービス is more about a promotional bargain, not necessarily clearing stock.
Compound of 出血 (bleeding, loss) + 大 (big) + サービス (service, discount). The phrase figuratively suggests the seller is 'bleeding' money by offering such a generous deal.