Final answer:
Enamel paint would be the better choice for a customer painting the kitchen who prefers a flat sheen but is worried about water spotting and cleanliness.
Step-by-step explanation:
The better choice of coating for a customer who prefers a flat sheen but is worried about water spotting and keeping walls clean would be an enamel paint. Enamel paints have a high-gloss finish, but they are also extremely durable and resistant to water spotting. They use heavy solvents, which help create a tough and protective coating.
Another option to consider would be powder coat paint. Although it is mostly applied to metal surfaces, it forms a tough and strong skin that is stronger than most other paints. However, it might not provide the flat sheen that the customer prefers.
In summary, for a customer looking for a flat sheen while being worried about water spotting and cleanliness, enamel paint would be the better choice.