Stop editing 500 products: rule-based discounts in WooCommerce

My wife Lena paints. Oils, acrylics, watercolors. Flowers, landscapes, the occasional cello or violin from her music series. Each painting is its own thing, photographed and listed on her store at artbylena.com . The catalog has crept past a hundred and twenty pieces and keeps growing. Last spring, two weeks out from Mother's Day, she decided to run a 20% sale on the flower paintings. The right move - flowers are what people buy for their mothers. She opened the WooCommerce admin and started edi