den Kunden: Singular oder Plural?

With n-nouns, the noun often looks the same in the singular and the plural, so the article tells you what is meant:

• den Kunden — the customer (Akkusativ singular) or the customers (Dativ plural)
• die Kunden — the customers (Nominativ/Akkusativ plural)
• dem Kunden — the customer (Dativ singular)

Only the Nominativ singular has no ending: Ein Kunde wartet.