Sold by the litre, not by the item
A graffiti remover is one product that exists as a one-litre bottle, a five-litre can and a drum, each at its own price. Modelled as separate products that is three listings competing with each other in search and three sets of copy to keep in step; modelled as an option on one product, the buyer picks the volume and the price follows.
That is the difference between a catalogue that can grow and one that has to be re-entered every time the range changes, and it is decided at the data level long before anything is designed.