1. Original bill: refers to the genuine original bill produced by the manufacturer or brand, which is the most formal and standard product. 2. Documentary: refers to products with unclear purchase channels or through intermediate layers, which have certain risks but relatively low prices. 3. Subsequent order: refers to the act of adding an order on the basis of the original order or documentary order, which belongs to the second purchase and is generally cheaper. 4. Imitation bill: refers to the cottage products whose appearance is similar to the original products, but whose quality, technology and materials are quite different. It belongs to pirated, fake and shoddy products.